The time between calls is exponentially distributed with a meantime between call

The time between calls is exponentially distributed with a meantime between calls of 10 minuted a) What is the probability that the time until the first call is less than 5 minutes b) What is the probability that the time until the first call is between 5 and 15 minutes c) Determine the length of an interval of time such that the probability of at least one call in the interval is 0.90 d) If there has not been a call in 10 minutes what is the probability that the time until the next call is less than 5minutes e) what is the probability that there are no call in the intervals from 10:00 to 10:05 from 11:30 to 11:35 and from 2:00 to2:05? f) What is the probability that the time until the third call is greater than 30 minutes? g) What is the mean time until the fifth call?