400 sq yards.
15.5 square yards = 140 square feet.
1 sq yard = 9 sq feet so 6400 sq yards = 6400*9 = 57600 sq feet.
Assuming the yards means square yards, there are 33 sq yd * 9 sq ft/sq yard = 297 sq feet.
depends on the depth that you need to cover the 1200 square feet (area) to. there are 3 foot to 1 yard (1 foot=3 yards). so 1 square foot = 9 square yards (3x3). 1200 square feet = 1200 x9 = 10,800 square yards. you then multiply the 10,800 by the amount of yards (depth) that you want to cover the area to.
9 sq feet = 1 sq yard so 15*20 = 300 sq ft = 33.33... sq yards