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.

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?