5.33 A complex electronic system is built with a certain number of backup components in its subsystems.

One subsystem has four identical components, each with probability 0.2 of failing in less than 1,000 hours. The subsystem will operate if any two or more of the four components are operating. Assuming the components operate independently, find the probability that a Exactly two of the four components last longer than 1,000 hours.
b The subsystem operates longer than 1,000 hours.