Question

Mrs. Thomas is designing a rectangular pool for her backyard. The width of the pool is 71/2 feet shorter than twice its length. The perimeter of the pool is 75 feet. What is the length of the pool?

Answer 1

L = length
W = width
71/2 = 35.5

The width of the pool is 35.5 ft shorter than twice the length
We can say
W = 2L - 35.5
to help connect the two variables

Then you'll use the perimeter of a rectangle formula
P = 2(L+W)

Plug in W = 2L-35.5
P = 2(L+W)
P = 2(L+2L-35.5)
P = 2(3L-35.5)
P = 6L - 71

Then plug in P = 75
P = 6L - 71
6L - 71 = P
6L - 71 = 75
Solve for L

Do you see how to finish up?