The contractor needs 8 pieces of 4-foot, 2 inch framing. A 10-foot lumber can be made into two pieces of framing. In order to complete the 8 pieces needed, the contractor needs to order 4 pieces of 10-foot long lumber.
So, 4 pieces x 10 feet = 40 feet of framing
The contractor actually only needs a total of 34 feet of framing, but lumber is usually cut and sold in even lengths by feet (such as 10, 12, 14 and 16 feet). And as stated in this question, the lumber availability was in 10-foot length.