Answer
3.5 gallons
Work Step by Step
1. Find the area of the deck with the formula A = lw.
A = 35*20 = 700
2. Each gallon covers 200 sq feet, so to determine how many gallons we need, we divide the area of the deck by 200:
700 $\div$ 200 = 3.5
We need 3.5 gallons.