Question 1008904
Perimeter P = 2L + 2W = 84.  We also have
L = 4W + 8
Now substitute that into the first equation and get
2(4W + 8) + 2W = 84
8W + 16 + 2W = 84
10W + 16 = 84
10W = 68
W = 6.8 m
L = 4(6.8) + 8 = 35.2 m