If my room is 24ft long and 18 ft wide and ceilings are 9ft high how many square yards of wallpaper will be needed for 4 walls?
So the area of all the walls will be:
$\displaystyle 2(24 \times 9) + 2(18 \times 9) = 432 + 324 = 756$ square foot (feet? I'm not familiar with the American system)
1 foot = 1/3 yards
1 square foot = 1/9 square yards
756 / 9 = 84
Therefore you will need 84 square yards of wallpaper.