A teacher would like to know how sleep impacts exam performance. For four students randomly selected from her class, she gathers data (reported in the table below) on how many hours of sleep they got the night before a recent exam and how many points (out of 100) they scored on that exam. She then performs a simple linear regression using this data.

Hours of sleep the night before the exam	Points (out of 100) scored on exam
3	60
6	70
9	80
7	100

(A) (8 pts) What is the dependent variable and what is the explanatory variable?

(B) (8 pts) What is the covariance between the dependent variable and the explanatory variable? Type your manual calculation.

(C) (8 pts) What is the variance of the explanatory variable? Type your manual calculation.

(D) (8 pts) What is the average impact of each additional hour of sleep on exam score? Type your manual calculation.

(E) (8 pts) Students who pulled an all-nighter and did not sleep at all the night before on average scored how many points on the exam? Type your manual calculation.