How can fix in smart contract written in solidity?

Question

TypeError: Invalid type for argument in function call. Invalid implicit conversion from address to address payable requested. selfdestruct(admin);

pragma solidity >=0.4.21 <0.6.0;
import "./DappToken.sol";
contract DappTokenSale{
    address admin;
    DappToken public tokenContract;
    uint256 public tokenPrice;
    uint256 public tokensSold;

    event Sell(address _buyer, uint256 _amount);

    constructor(DappToken _tokenContract, uint256 _tokenPrice) public {
        //Assign an admin
        admin = msg.sender;
        //token Contract
        tokenContract = _tokenContract;
        //Token Price
        tokenPrice = _tokenPrice;
    }
    // multiply function
    function multiply(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x);
    }
    // Buy Token
    function buyTokens(uint256 _numberOfTokens) public payable{
        // Reqiured that value is equal to tokens
        require(msg.value == multiply(_numberOfTokens, tokenPrice));
        // Required that the contract has enough token
        require(tokenContract.balanceOf(address(this)) >= _numberOfTokens);    
        // Required that a trnasfer is successfuly
        require(tokenContract.transfer(msg.sender,_numberOfTokens));
        // keep track of number of token sold
        tokensSold += _numberOfTokens;

        // Trigger sell event
        emit Sell(msg.sender, _numberOfTokens);
    }

    // Ending Token DappTokenSale
    function endSale() public {
        // Require admin
        require(msg.sender == admin);
        // Transfer remaining dapp token to admin
        require(tokenContract.transfer(admin, tokenContract.balanceOf(address(this))));
        // UPDATE: Let's not destroy the contract here
        // Just transfer the balance to the admin
        // admin.transfer(address payable(this).balance);
        // selfdestruct(address payable admin);
        // selfdestruct(address payable admin);
        //address payable adminAddress = address(uint160(admin));
        selfdestruct(admin);
    }
}

Answer 1

Change line 4 to:

address payable admin;

Hope it helps.

Answer 2

=> add this code in first line // SPDX-License-Identifier: MIT

=> Change address admin; to address payable admin;

=> add emit before every transaction event like emit Sell(msg.sender, _numberOfTokens);