The exam for course A is worth 25% of your grade and the exam for course B is worth 50% of your grade. The first hour you spend on studying for either exam will increase your score on it by 10 percentage points, the second hour will increase your grade on it by an additional 9 percentage points, the third hour will increase your grade on it by an additional 8 percentage points, and so forth. How will you allocate your time? Explain your answer in terms of marginal analysis.