Suppose that a market research analyst for a cell phone company conducts a study of their customers who exceeds the time

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Suppose that a market research analyst for a cell phone company
conducts a study of their customers who exceeds the time allowance
included on their basic cell phone contract. The analyst finds that
for those people who exceed the time included in their basic
contract, the excess time used follows an exponential distribution
with a mean of 30 minutes. Consider a random sample of 65 customers
who exceed the time allowance included in their basic cell phone
contract. In an exponential distribution mean and standard
deviation values are same.
Find the probability that the mean excess time used by the 65
customers in the sample is in between 1500 and 1680 seconds.