ICO contract inherit from openzeppelin ERC20

[CodeWithUmair]

I'm inheriting this ICO contract directly from openzeppelin see:

I got an error in line no. 80. where I store tokens in balances[msg.sender]. But it is problematic because I haven't created any balance or founder variables; I'm just inheriting ERC20 from openzeppelin, so what is a balances or founder variable in my case?

see this picture:

Please give me an answer to this problem. I need to make the invest function. 😏

[Umair-3]

Yes I got this same error, Please help us in this "balances" argument which is in the function of "balanceOf" in ERC20. 😯