Simple calculus question?

Question

Suppose that a rectangle has a perimeter of 25 meters. Express the area A(x) of the rectangle in terms of the length x of one of its sides.

A(x) =....

how do you do this, step by step?

Answer 1

A rectangle's perimeter is 2L + 2W = 25

say the Length is x.  Then the width (in terms of x) is (25 -2x)/2

Area = Lenghth X Width

in our terms

A(x) = x(25 - 2x)/2

Answer 2

A(x)= X x (X/2)

I'm bad at math. I want tp see someone answer