I'm having trouble with this textbook question and would be extremely grateful if someone solved and showed me the steps to the solution of this question.

1. A professor decides to run an experiment to measure the effect of time pressure on final exam scores. He gives each of the 400 students in his course the same final exam, but some students have 90 minutes to complete the exam, while others have 120 minutes. Each student is randomly assigned one of the examination times, based on the flip of a coin. Let Y denote the number of points scored on the exam by the ith student (0