A gallon of paint can cover 400 square feet. To the nearest half gallon, find how much paint will be needed to paint two coats on the walls and ceiling of room that is 20 feet long, 18 feet wide and 8 feet high

I think that this is right, but I assumed that the ceiling has the same dimensions as the wall you would need 4 gallons for 2 coats.

Work:

20x8 = 160 (square feet for 1 wall)

160x5=800 (i assumed there are 4 walls and 1 ceiling)

800x2=1600 (you need 2 coats)

1600/400=4 (each gallon includes 400 square feet)