using the two existing corner sides of an existing wall, what is the maximum rectangular area that can be fenced by a fencing material 30 ft long?

Answer 1

Assuming the two walls meet at a right angle,

x+y = 30
a = xy = x(30-x)
this is just a parabola, with vertex at x=15. As usual, the area is a square.

You can take the derivative if you want, but no calculus needed here...

Answer 2

225

Answer 3

just testing this account after a year