Bob and Betty make bird houses and mailboxes in their craft shop near Gatlinburg. Each bird house requires 3 hr of work from Bob and 1 hr from Betty. Each mailbox requires 4 hr of work from Bob and 2 hr of work from Betty. Bob cannot work more than 48 hr per week and Betty cannot work more than 20 hr per week. If each birdhouse sells for $12 and each mailbox sells for $20, then how may of each should they make to maximize their revenue? (Hint: Let x = the number of birdhouses and let y = the number of mailboxes, and write one equality for the amount of time Bob can work and another inequality for the amount of time Betty can work. The objective function for this problem is C - 12x + 20y) birdhouses mailboxes