W= width= substitute height for width in the perimeter formula
L= length
Perimeter= 2L + 2W
plug in numbers you know
40.6= 2L + 2(7.8)
40.6= 2L + 15.6
subtract 15.6 from both sides; it becomes 0 on the right side
25= 2L
divide both sides by 2
12.5= L
ANSWER: The length is 12.5 miles
Hope this helps! :)
