I got 2 more intense problems like this. Can someone show me the way for each step so I can follow along with the other problems I have to do? ThankS!

Question

A gardener has 40 feet of fencing with which to enclose a garden adjacent to a long existing wall. The gardener will use the wall for one side and the available fencing for the remaining three sides.

If the sides perpendicular to the wall have length x feet, which of the following (A, B, C, or D) represents the area A of the garden?

A. A(x) = –2x^2 + 20x
B. A(x) = –2x^2 + 40x
C. A(x) = 2x^2 – 40x
D. A(x) = x^2 – 40x

The area function is a quadratic function and so its graph is a parabola.

Does the parabola open up or down?

Find the vertex of the quadratic function A(x). Show work.

Use the work in the previous parts to help determine the dimensions of the garden which yield the maximum area, and state the maximum area. (Fill in the blanks below. Include the units of measurement.)

The maximum area is ?

when the sides perpendicular to the wall have length x = ?
and the side parallel to the wall has length ?.

Answer 1

http://www.wtamu.edu/academic/anns/mps/math/mathlab/col_algebra/col_alg_tut34_quadfun.htm

Answer 2

For the perpendicular sides, the distance is x; there are two sides so that is 2x if added together. Since the fence is the third side, then the fourth must be 40-2x for its length. Therefore, the area is x(40-2x).
Use the site I posted above to find the vertex and if the parabola opens up or down.