Simultaneous Equations: Area of a Rectangle

Hello everyone!

The textbook out of which I am studying provides examples of simultaneous equation problems, but nothing similar to what is being required here. Does anyone know what to do in parts c and d? I have drawn a diagram and done a and b, but I cannot solve the latter two. Much help is appreciated! Thank you in advance to any mathematicians out there.

(Happy)(Happy)(Happy)(Happy)

*A rectangular enclosure is to be fenced so that its perimeter is 60 metres. *

*a. If w is the length of the rectangle, what is its length in terms of w?*

*l = 30 - w*

*b. Write an expression for A, the area of the rectangular enclosure.*

*A = w(30 - w)*

*c. What value of w will give the greatest area of the rectangular enclosure?*

*d. What is the greatest area the rectangular enclosure can have?*