A vending machine dispenses hot chocolate or coffee. service time is 30 seconds per cup and is constant. Customers arrive at a mean rate of 72 per hour, and this rate is poisson-distributed. a. determine the average number of customers waiting in line. (round your answer to 2 decimal places.) b. determine the average time customers spend in the system. (do not round intermediate calculations. round your answer to 2 decimal places.) c. determine the average number of customers in the system. (do not round intermediate calculations. round your answer to 2 decimal places.)