Let X be the random variable denoting the number of bad tires in the school vehicles circulating in a certain city, whose probability function is given by: k(5 - x) P(X = x) = 10, x = 0,1,2,3,4. 0, in another case a) Find the value of k b) What is the probability that a randomly selected school vehicle has two bad tires? c) Find the expectation and variance of X