The median of a data set is the middle number. To find this value, you'll need to order your data set from smallest to largest and then cross off values equally from each end until you reach the middle. In the case there are two numbers in the middle, you will find the mean/average of those two numbers.
7, 9, 11, 14, 18, 20, 30, 35
9, 11, 14, 18, 20, 30
11, 14, 18, 20
14, 18
Average of 14 and 18 = 16
Answer: C. 16
Hope this helps!