The waiting time, in hours, between successive speeders spotted by a radar unit is a continuous random variable with cumulative distribution function f(x) = { 1 - 1/e^(8x), x >= 0; 0, elsewhere. Find the probability of waiting less than 12 minutes between successive speeders a. using the cumulative distribution function of X. b. using the probability density function of X. c. Find the expectation E[X] and Var(X) of the random variable X.