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ERC20Token.sol

pragma solidity 0.5.1;


contract ERC20Token {
    string public name;
    mapping(address => uint256) public balances;
    
    function mint() public {
        balances[tx.origin] ++;
    }
}


contract Purchase {
    address payable public wallet;
    address public token; 
    
    constructor(address payable _wallet, address _token) public {
       wallet = _wallet;
       token = _token;
    }
    
    function buyToken() public payable {
        ERC20Token _token = ERC20Token(address(token));
        _token.mint();
        wallet.transfer(msg.value);
    }
}

MyContract.sol

pragma solidity  0.5.1;

contract MyContract {
    uint256 public count = 0;
    mapping (uint => Person) public people;
    address owner;
    
    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }
    
    struct Person {
        string firstName;
        string lastName;
    }
    
    
    constructor() public {
        owner = msg.sender;
    }
    
    function addPerson(string memory _firstName, string memory _lastName) public onlyOwner {
        incrementCount();
        people[count] = Person(_firstName, _lastName);
    }
    
    function incrementCount() internal {
        count += 1;
    }
}

Token.sol

pragma solidity 0.5.1;


contract Token {
    mapping (address => uint256) public balances;
    address payable wallet;
    
    event Purchase (
        address _buyer, 
        uint256 _amount
    );
    
    constructor(address payable _wallet) public {
        wallet = _wallet;
    }
    
    function() external payable {
        buyToken();
    }
    
    function buyToken() public payable {
        // Buy a token 
        balances[msg.sender] += 1;
        
        
        // Send ether to the wallet 
        wallet.transfer(msg.value);
        
        // Emit event 
        emit Purchase(msg.sender, 1); 
    }
}