Strong earthquakes occur according to a Poisson process in a metropolitan area with a mean rate of once in 50 years. There are three bridges in the metropolitan area. When a strong earthquake occurs, there is a probability of 0.3 that a given bridge will collapse. Assume the events of collapse between bridges during a strong earthquake are statistically independent; also, the events of bridge collapse between earthquakes are also statistically independent. (a) What is the probability of at most one strong earthquake occurring in this metropolitan area within the next 20 years? (b) During a strong earthquake, what is the probability that exactly one of the three bridges will collapse? (c) What is the probability of "no bridge collapse from strong earthquakes" during the next 20 years?