Here is the equation:

Since both decimals are negative, the answer will be positive.
- Negative times Negative = Positive
Divide both sides by -3.9 to leave the variable alone:

r is equal to 4 → r = 4
Perimeter formula
p = 2l + 2w
I reverse left-right side
2l + 2w = p
Move 2l to the right
2l + 2w = p
2w = p - 2l
Move 2 to the right
2w = p - 2l
w = (p - 2l)/2
Summary
p = 2l + 2w
2l + 2w = p
2w = p - 2l
w = (p-2l)/2
I might be wrong but it might be 62
Answer- 42646.50 pounds
Area of flat surface = Area of rectangle + area of triangle
= 12.9*25 + 1/2* 7.2* 25
= 162.5 feet^2
Force exerted by wind =0 .004 * Area * velocity^2
= 42646.50 pounds