(8). Japan is one of the country where earthquake occurs most frequently. Let random variable X be the waiting time (in hour) until next earthquake occurs at Japan (count from the previous earthquake stops), X has an exponential distribution with =0.2=0.2. 1(2). Find the expected value and variance of the waiting time X. 2(6). For a sample of 36 randomly selected earthquakes, find the probability that sample mean waiting time is more than 4 hours.