Answer :
ok
P = 90 m
length = l
width = w
Equation
l = 2w + 6
P = 2l + 2w
Substitution
90 = 2(2w + 6) + 2w
90 = 4w + 12 + 2w
90 - 12 = 6w
78 = 6w
w = 78/6
w = 13 m
l = 2(13) + 6
l = 26 + 6
l = 32
Test
90 = 2(32) + 2(13)
90 = 64 + 26
90 = 90
It's correct
Length = 32m Width = 13 m