A complex electronic system has 4 identical components, and each component operates for an Exponentially distributed time with a mean of 2000 hours. Assume that the components operate independently. The system will operate if at least 2 of the 4 components are operating. (a) [5 pts] Find the probability that exactly 2 of the 4 components last longer than 1000 hours. [b] [3 pts] Find the probability that the system operates longer than 1000 hours. {c} [4 pts] Calculate the mean and variance of the sum of operating times of all 4 components