A 20-ft by 40-ft swimming pool is surrounded by a deck d feet wide. What is the area of the deck?

Answer 1

area of pool = (20)(4) = 800 ft^2

length of pool plus deck = 40+2d
width of pool plus deck = 20+2d
Area of whole thing = (40+2d)(20+2d)
= 800 + 120d + 4d^2

area of deck = 4d^2 +120d + 800- 800
= 4d^2 + 120d