4. Batman enjoys baking cakes and knitting sweaters. It takes him 2 hours to bake a cake, and 6 hours to knit a sweater. He has 12 hours of free time per week, which he uses to bake and knit. Which of the following is true about his opportunity cost? a. The opportunity cost of baking a cake is 1/3 of a sweater. b. The opportunity cost of baking a cake is 3 of a sweaters. c. The opportunity cost of baking a cake is 4 sweaters. d. The opportunity cost of baking a cake is 6 sweaters.