Standard Deviation Calculation

In a recent study, the following data was collected representing the number of hours 20 students spent studying in a week:

10, 15, 20, 15, 10, 25, 30, 20, 15, 10, 20, 15, 10, 30, 25, 20, 10, 15, 20, 30

From this data, calculate the standard deviation.