The area of a rectangle is the product of its length and width:
(7 yds)(3 yds) = 21 square yds.
We must convert this to square feet. Note that 1 sq yd = 27 sq ft.
Thus, (21 sq yd) times (27 sq ft / 1 sq yd) = 21(27) sq ft. Finish this by multiplying 21 and 27 together. Be sure to include the units of measurement.