The width of a rectangle is 15 cm less than the length. the perimeter is 78 cm. find the rectangle's dimensions

Length (L) : L

width (w) : L - 15

Perimeter (P) = 2L + 2w

78 = 2 (L) + 2 (L - 15)

78 = 2L + 2L - 30

78 = 4L - 30

108 = 4L

27 = L

width (w) : L - 15 = 27 - 15 = 12

Answer: width = 12 cm, length = 27 cm