Please solve with step by step to gain the answer 3.012

It is claimed that the expected length of time some computer part may work before requiring a reboot is 26 days. In order to examine this claim 80 identical parts are set to work. Assume that the distribution of the length of time the part can work (in days) is Exponential. The central region that contains 70% of the distribution of the average is of the form E(X) c, where E(X) is the expectation of the sample average. The value of c is (You are asked to apply the Normal approximation to the distribution of the average of the 80 parts that are examined. The answer may be rounded up to 3 decimal places of the actual value.)