The distance between major cracks in a highway follows an exponential distribution with mean of four miles.

The distance between major cracks in a highway follows an exponential distribution with mean of four miles.A) What is the probability that there are no major cracks in a 12-mile stretch of the highway?B) What is the probability that there are three major cracks in a 12-mile stretch of the highway?C) What is the standard deviation of the distance between major cracks?