calculus question involving optimization?

So, we look at the equation for perimeter of a rectangle. The perimeter of our rectangle is 2x+2y=148 and we solve for one variable: x + y = 74, x = 74 - y.

Now, we look at the equation for area of a rectangle, ours will be x y = a. Replace x with y, so we get one single variable,

(74 - y) y = a

now simplify,

74y - y^2 = a.

now derive,

74 - 2y = a

Now we find the relative extrema of the equation by substituting the derivative of area with zero

74 -2y = 0

Solve

y = 37

Because I don't want to waste your time with checking, I will simply plug this back into our perimeter equation and solve for x.

2x + 2(37) = 148

2x + 74 = 148

2x = 74

x = 37

So your answer to this are the dimensions 37 x 37, and the area of this is 1369 sqft.

That has the maximum area? Of what?