A store estimates that between 5:00pm and 6:00pm each weekday, an average of 12 customers enters any given checkout line. Suppose you are a cashier in that store. What is the probability:

a) That at most 15 customers enter your line between 5:00pm and 6:00pm?

b) That exactly 8 customers enter your line between 5:00pm and 6:00pm?

c) That more than 20 customers enter your line between 5:00pm and 6:00pm