A craftsman named William Barnes builds two kinds of birdhouses, one for wrens and a second for bluebirds. Each wren birdhouse takes 4 hours of labor and 4 units of lumber. Each bluebird house requires 2 hours of labor and 12 units of lumber. The craftsman has available 72 hours of labor and 120 units of lumber. Wren houses yield a profit of $10 each and bluebird houses yield a profit of $15 each. The aim of the objective function for William should be to the objective value. The optimum solution is: Number of wren houses to be produced = (round your response to two decimal places)