We can use the overlapping sets formula: Total = Group 1 + Group 2 - Both + Neither. Since we're dealing in percents, total = 100. Group 1, American-made movies, is 60, while Group 2, comedies, is 35. Neither is 30, so we can solve for both:

100 = 60 + 35 - B + 30

100 = 125 - B

B = 25, choice (C).