real numbers \(y\) and \(y - 1\) so you will definitely get answer.
it just of the form : \(area - perimeter\).
we can cancel out or add any two like terms if and only if both the like terms are of the same degree.
\(ex : 5y - 3y = 2y\). here \(5y\) and \(3y\) are of same degree that is \(1\) so you can subtract them or you can add them .
but what about \((x^3 - x)\) ?
solution : you cannot subtract them nor you can add them. the reason is that the first \(x\) is of the degree \(3\) where as the second \(x\) is of the degree \(1\).
what about 