Answer:
A) Susan has an absolute advantage in solving math problems, because she can solve 15 problems per hour while Tom can only solve 10.
B) They can both benefit from trade because of comparative advantages, Susan should solve math problems and Tom should write short stories.
C) Susan would gain if she can trade math problems for short essays, for example if Susan solves 12 math problems for Tom in exchange for 2 short stories, then both would gain from trade. Susan would gain 3 math problems and Tom would gain 2.