The median of a list is the middle value, when all the values in the list are put in order from smallest to biggest. Here, we are concerned with the 82 high school students --- for each, we have a number: the number of hours of TV they watched last week. Since 82 is an even number, the median would be the average of the middle two numbers, the average of 41st and 42nd numbers.

1st number
2nd number
3rd number
.
.
.

.
.
.
80th number
81st number
82nd number


Here, we don't have any of the individual numbers, only their groupings, but we can figure out where the 41st and 42nd numbers would be. Clearly, the first column is 13 units high, we means it contains the first 13 numbers on the list. The second column is 35 units high --- 13 + 35 = 48, so that's the first 48 numbers on the list. If we count all the way down to the 48th number on the list, that means we have already passed the 41st and 42nd numbers, which means the median must be included in the numbers in the second column. Answer = (B).