A cafeteria serving line has a coffee urn from which customers serve themselves. Arrivals at the urn follow a Poisson distribution at the rate of three per minute. In serving themselves, customers take about 15 seconds, exponentially distributed.

a.How many customers would you expect to see, on average, at the coffee urn?

b.How long would you expect it to take to get a cup of coffee?

d.What is the probability that three or more people are in the cafeteria?(Do not round intermediate calculations. Round your answer to 1 decimal place.)

e.If the cafeteria installs an automatic vendor that dispenses a cup of coffee at a constant time of 15 seconds, how many customers would you expect to see at the coffee urn (waiting and/or pouring coffee)?(Round your answer to 2 decimal places.)

f.If the cafeteria installs an automatic vendor that dispenses a cup of coffee at a constant time of 15 seconds, how long would you expect it to take (in minutes) to get a cup of coffee, including waiting time?(Round your answer to 2 decimal places.)

I'm having a lot of trouble d,e,and f