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contracts...subquest-8a.sol

pragma solidity >=0.7.0 <0.9.0;

contract SmartBankAccount {

    uint totalContractBalance = 0;

    function getContractBalance() public returns(uint){
        return totalContractBalance;
    }
    
    mapping(address => uint) balances;
    mapping(address => uint) depositTimestamps;
    
    function addBalance() public payable {
        balances[msg.sender] = msg.value;
        totalContractBalance = totalContractBalance + msg.value;
        depositTimestamps[msg.sender] = block.timestamp;
    }
    
    function getBalance(address userAddress) public returns(uint){
        uint principal = balances[userAddress];
        uint timeElapsed = block.timestamp - depositTimestamps[userAddress]; //seconds
        return principal + uint((principal * 7 * timeElapsed) / (100 * 365 * 24 * 60 * 60)); //simple interest of 7%  per year
    }
    
    function withdraw() public payable {
        address payable withdrawTo = payable(msg.sender);
        uint amountToTransfer = getBalance(msg.sender);
        withdrawTo.transfer(amountToTransfer);
        totalContractBalance = totalContractBalance - amountToTransfer;
        balances[msg.sender] = 0;
    }
    
}