A craftsman builds two kinds of birdhouses, one for wrens (X1), and one for bluebirds (X2). Each wren birdhouse takes four hours of labor and four units of lumber. Each bluebird house requires two hours of labor and twelve units of lumber. The craftsman has available 60 hours of labor and 120 units of lumber. Wren houses profit $6 each and bluebird houses profit $15 each. Show your work. a. What is the optimal solution for X1 and X2? b. What is the max profit?