4.7.5 (video solution) the time between calls to a plumbing supply business is exponentially distributed with a mean time between calls of 18 minutes. (a) what is the probability that there are no calls within a 30-minute interval? enter your answer in accordance to the item a) of the question statement (round your answer to 4 decimal places.) (b) what is the probability that at least one call arrives within a 10-minute interval? enter your answer in accordance to the item b) of the question statement (round your answer to 4 decimal places.) (c) what is the probability that the first call arrives within 5 and 10 minutes after opening? enter your answer in accordance to the item c) of the question statement (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. enter your answer in accordance to the item d) of the question statement minutes (round your answer to 2 decimal places.)