The following table gives the frequency distribution of the number of hours spent last week on cell phones (making phone calls and texting) by all 100 students of the tenth grade at a school. 

Hours per Week               Number of Students

0 to less than 4……………………...  14

4 to less than 8………………………  18

8 to less than 12…………………….   25

12 to less than 16……………………  18

16 to less than 20……………………  16

20 to less than 24……………………  9

Find the mean, variance, and standard deviation.