interface.sol

pragma solidity ^0.8.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
}

contract Token {
    
    // state variable called ERC20ContractAddress that represents the address of the ERC20 contract
    address private constant ERC20ContractAddress = CONTRACTADDRESS;
    
    
    // to access the functions in the ERC20 contract
    // use the interface declared above and wrap the ERC20 contract address in ()  
    IERC20  TokenInstance = IERC20(ERC20ContractAddress) ;

    function getTotalSupply() external pure returns(uint) {
        return TokenInstance.totalSupply();
  }

  function getBalanceOf() external pure returns(uint) {
        return TokenInstance.balanceOf();
  }
  

}