A builder has 80 feet of fencing to create an enclosure adjacent to a long existing wall. He 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 represents the area A of the enclosure?

To find the area of the enclosure, we need to determine the length of the two sides perpendicular to the wall and the length of the side parallel to the wall.

Let's first find the length of the side parallel to the wall. Since the total length of fencing available is 80 feet, and one side is the existing wall, the remaining three sides must add up to 80 feet. Therefore, the length of the side parallel to the wall is (80 - x) feet.

Now, let's calculate the area of the enclosure. The area of a rectangle is given by its length multiplied by its width. In this case, the length of the enclosure is x feet, and the width is (80 - x) feet.

So, the area A of the enclosure can be represented as:

A = x * (80 - x)

This is the answer to the question. The area A of the enclosure is x * (80 - x).