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Destroyable.sol

import "./Ownable.sol";
pragma solidity 0.5.12;

contract Destroyable is Ownable{
    function close() public onlyOwner { //onlyOwner is custom modifier
    address payable ownerpayable = address(uint160(owner));
        selfdestruct(ownerpayable);  // `owner` is the owners address
    }    
}

Ownable.sol

pragma solidity 0.5.12;

contract Ownable{

    address public owner;

    modifier onlyOwner(){
        require(msg.sender == owner);
        _; //Continue execution
    }
    
    constructor() public{
        owner = msg.sender;
    }

}

People.sol

import "./Ownable.sol";
import "./Destroyable.sol";
pragma solidity 0.5.12;


contract HelloWorld is Ownable, Destroyable{

    struct Person {
      uint id;
      string name;
      uint age;
      uint height;
      bool senior;
    }

    event personCreated(string name, bool senior);
    event personDeleted(string name, bool senior, address deletedBy);
     //Create an event called PersonUpdated that is emitted when a persons information is updated. The event should contain both the old and the updated information of the person. 
    event PersonUpdated(string nameold, string name, uint ageold, uint age, uint heightold, uint height) ;

    uint public balance;

    modifier costs(uint cost) {
        require(msg.value >= cost);
        _; //Continue execution        
    }



    mapping (address => Person) private people;
    address[] private creators;

    function createPerson(string memory name, uint age, uint height) internal {
        require(age < 150, "Age needs to be below 150");
        balance += msg.value;
        //This creates a person
        Person memory newPerson;
        newPerson.name = name;
        newPerson.age = age;
        newPerson.height = height;

        if(age >= 65){
           newPerson.senior = true;
       }
       else{
           newPerson.senior = false;
       }

        insertPerson(newPerson);
        creators.push(msg.sender);

        assert(
            keccak256(
                abi.encodePacked(
                    people[msg.sender].name,
                    people[msg.sender].age,
                    people[msg.sender].height,
                    people[msg.sender].senior
                )
            )
            ==
            keccak256(
                abi.encodePacked(
                    newPerson.name,
                    newPerson.age,
                    newPerson.height,
                    newPerson.senior
                )
            )
        );
        emit personCreated(newPerson.name, newPerson.senior);
    }
    function insertPerson(Person memory newPerson) private {
        address creator = msg.sender;
        people[creator] = newPerson;
    }
    function getPerson() public view returns(string memory name, uint age, uint height, bool senior){
        address creator = msg.sender;
        return (people[creator].name, people[creator].age, people[creator].height, people[creator].senior);
    }
    function deletePerson(address creator) public onlyOwner {
      string memory name = people[creator].name;
      bool senior = people[creator].senior;

       delete people[creator];
       assert(people[creator].age == 0);
       emit personDeleted(name, senior, owner);
   }
   function getCreator(uint index) public view onlyOwner returns(address){
       return creators[index];
   }

   function withdrawAll() public onlyOwner returns(uint) {
       uint toTransfer = balance;
       balance = 0;
       msg.sender.transfer(toTransfer);
   }
  

}

token.sol

import "./Ownable.sol";
pragma solidity 0.5.12;

contract ERC20 is Ownable{

    mapping (address => uint256) private _balances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

        constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    function name() public view returns (string memory) {
        return _name;
    }

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    function mint(address account, uint256 amount) public onlyOwner{
        _totalSupply += amount;
    }

    function transfer(address recipient, uint256 amount) public returns (bool) {
        uint toTransfer = _balances[msg.sender];
        _balances[msg.sender] = toTransfer - amount;
        _balances[recipient] += amount;
        return true;
    }
}

Workers.sol

import "./People.sol";

pragma solidity 0.5.12;


contract Workers is HelloWorld{
    mapping(address => uint) salary;
    
    function createWorker(string memory name, uint age, uint height) public {
        require(age < 75);
        createPerson(name, age, height);
        salary[msg.sender] = 25000;
    }
    function fireWorker() public {
        deletePerson(msg.sender);
    }
     
}