Step-by-step explanation:
the perimeter is
2×length + 2×width = 86
length = 3×width
now we use the second equation as variable identity in the first equation :
2×3×width + 2×width = 86
6×width + 2×width = 86
8×width = 86
width = 86/8 = 43/4 = 10.75 cm
length = 3×width = 3×10.75 = 32.25 cm
