8 * 4 = <<8*4=32>>32 square feet
20 * 32 = <<20*32=640>>640 square feet
5040 - 640 = <<5040-640=4400>>4400 square feet
There are 42 - 20 = <<42-20=22>>22 remaining units
4400/22 = <<4400/22=200>>200 square feet
One of the remaining units is 200 square feet.
#### 200