the time between calls to a plumbing supply business is exponentially distributed with a mean time between calls of 16 minutes. (a) what is the probability that there are no calls within a 30-minute interval? (round your answer to 4 decimal places.) (b) what is the probability that at least one call arrives within a 10-minute interval? (round your answer to 4 decimal places.) (c) what is the probability that the first call arrives within 5 and 10 minutes after opening? (round your answer to 4 decimal places.) (d) determine the length of an interval of time such that the probability of at least one call in the interval is 0.90. minutes (round your answer to 2 decimal places.)