Question 100755
There are 3 ft in 1 yd, so to convert yards to feet multiply 3. That is 2 yd = 6 ft.

If the width is 150 ft, then divide by 3 to get yds.  150 ft / 3 ft/yd = 50 yd

What is the length? Well, we know the area is 12,750 sq yd. And we know A=W*L, as you said. So 12,750 = 50 * L. Therefore, L = 12,750 / 50 = 2,550 yd (which is a long field indeed.)

To get the length in ft, multiply by 3:  3 ft/yd * 2550 yd = 7650 ft

Finally, 1 sq yd measures 3 ft by 3 ft, so it's 9 sq ft. Given there are 12,750 sq yd, then multiply by 9 to get the sq ft.