Answer
12 iTunes songs
24 utils
48 utils
Work Step by Step
opportunity cost game=$\frac{price\ game}{price\ book}=\frac{12}{1}=12\ books$
marginal cost game=$\frac{price\ game}{price\ book}\times MU_b=\frac{12}{1}\times2=24 utils$
marginal benefit game=marginal utility game=48 utils