Need Help ASAP!

This is due within the hour and i still cant figure out why my answers are incorrect. please help! will give a thumbs up!

Many of a bank's customers use its automatic teller machine to transact business after normal banking hours. During the early evening hours in the summer months, customers arrive at a certain location at the rate of one every other minute. This can be modeled using a Poisson distribution. Each customer spends an average of 90 seconds completing his or her transactions. Transaction time is exponentially distributed

a. Determine the average time customers spend at the machine, including waiting in line and completing transactions. (Do not round Intermedlate calculations. Round your answer to the nearest whole number.)

b. Determine the probability that a customer will not have to wait upon arriving at the automatic teller machine. (Round your answer to 2 decimal places.)

c. Determine the average number of customers waiting to use the machine. (Round your answer to 2 declmal places.)