Sisters Sharon and Karen enjoy sleeping. Let X represent the number of hours Sharon sleeps each night, and let Y represent the number of hours Karen sleeps each night. The mean of X is 7.9, and the mean of Y is 8.4. Which answer choice correctly calculates and interprets the mean of the sum, S = X + Y?

Mu Subscript s Baseline = 0.5; the mean amount of sleep Sharon and Karen get is 0.5 hours nightly.
Mu Subscript s Baseline = 8.15; the mean amount of sleep Sharon and Karen get is 8.15 hours nightly.
Mu Subscript s Baseline = 8.15; Sharon and Karen can expect to sleep a total of 8.15 hours, on average, nightly.
Mu Subscript s Baseline = 16.3; Sharon and Karen can expect to sleep a total of 16.3 hours, on average, nightly.