Function.sol

pragma solidity ^0.8.0;

contract MyContract {
    uint public myNumber;
    
    function setNumber(uint _number) public {
        myNumber = _number;
    }
}

Function2.sol

pragma solidity ^0.8.0;

contract Function {
    
    function add (uint _a, uint _b) external pure returns(uint) {
        return _a + _b;
    }
}