Ruby !! Method withdraw Help?

I just try to write this code but every time get below message.

Error Message: <Internal error: TypeError: FUNCTION_TABLE[HEAP[((HEAP[(f & (intermediate value))] + 4) & (intermediate value))]] is not a function>

I write this code in Ruby compiler :

def account.withdraw

@balance=@balance-amount

end

account.withdraw!(100)

Instructions

How to access the instance variable, but how do we change the value? This is where variable assignment comes in. How can i implement the withdraw! method on account object, which takes one parameter amount and reduces the balance by the specified amount? After defining the method, how can i ahead and withdraw 100 dollars from the account and check the balance.

Hint 1

The code @balance = @balance - amount reduces the amount from @balance.

Hint 2

Then call the method withdraw! on the account object - account.withdraw!(100)