Each year the water of a stream, river or lake peaks at some level, which may cause flooding of surrounding lands. In any given year, a flood will occur in a river when the maximum annual river stage exceeds 80 feet. a) If the probability that the maximum annual river stage exceeds 80 feet is 0.02, find the probability that the first flood will occur for the first time on the tenth year after this year. (4 marks) b) Suppose that the maximum annual river stage follows an exponential distribution with mean 25 feet. Find the return period of a flood.