Question 791164
P = 2w + 2L
L = 2w -1

40 = 2w + 2(2w -1)
40 = 2w + 4w -2
40 + 2 = 6w -2 + 2
42 = 6w
42/6 = 6w/6
7 = w
width = 7 feet
length = 2(7) -1
       = 14 -1
       = 13 feet

check: 
40 = 2(7) + 2(13)
40 = 14 + 26
40 = 40