The perimeter of a rectangular box is 42cm. The length is 13 cm. Find its area.
A
112cm2
B
104cm2
C
140cm2
D
121cm2
Correct Answer: 104cm2
2(a + b) = 42 ⇒ 2(13 + b) = 42 ⸫ b = 8 area = ab = 13 × 8 = 104 cm2