Arectangular deck has an area of 320ft^2. the length of the deck is 4 feet longer than the width. find the dimensions of the deck. solve by completing the square.

A = L * W
A = 320
L = W + 4

320 = W(W + 4)
320 = W^2 + 4W
W^2 + 4W = 320
W^2 + 4W + 4 = 320 + 4
(W + 2)^2 = 324
W + 2 = (+-) sqrt 324
W = -2 (+-) 18

W = -2 + 18 = 16 ft <== this is the width
W = -2 - 18 = -20not this one because it is negative

L = W + 4
L = 16 + 4
L = 20 ft <=== this is the length

in summary...the width is 16 ft and the length is 20 ft