Study time. Let X be the time (in hours) that Stephen spends studying on one particular day

Question:

Study time. Let X be the time (in hours) that Stephen spends studying on one particular day during "dead week" (the nickname for the week before final exams). Then X has density 1/4e-x/4. Let Y be the number of hours that Stephen spends studying for all 7 days during "dead week." Assume that the time spent studying on distinct days is independent.
a. Find E(Y).
b. Find Var("K).