A = L * W
A = 20 * 24
A = 480 sq ft.....so her garden is 480 sq ft.
1 qt of fertilizer covers 300 sq ft....so how many quarts will cover 480 sq ft.
set this up as a proportion
1/300 = x / 480....1 qt to 300 sq ft = x qts to 480 sq ft
cross multiply
(300)(x) = (1)(480)
300x = 480
x = 480/300
x = 1.6.....so Danielle will need 1.6 qts to cover her garden <==