As you can see, I already answered part A. That part is easy, like kindergarten level. But I don't remember learning how to do part B, so if someone could explain it I would be very grateful.

Length: 10 units.

Width:6 units

Step-by-step explanation:

Part a has 1 unit =40 yards. When we have 1 unit = 20 yards, we have divided the original numbers, 40, in half, getting 20. That means that we need to double the original amount of units, like you see above.