To repair his sprinkler system, Tony needs a total of 20 5/16 inches of PVC pipe. He has on hand pieces that measure 2 1/4 inches, 3 7/8 inches, and 4 1/4 inches in length. If he can combine these pieces and use them in the repair, how long a piece of PVC pipe will Tony need to purchase to repair his sprinkler system?

Write an expression that will solve the problem and then evaluate the expression.