A local bus company wants to estimate if the major travel line from a local city to the capitol is a profitable route. The number of passengers and the number of corresponding trips made during a two-month period are recorded in the following table:

Passengers 0 6 10 10 6 20 20 6 30 30 6 40 40 6 50 50 6 60 Trips 23 21 2 6 5 4

a. Estimate the mean number of passengers.

b. Estimate the sample variance and standard deviation.