Bill Borde, top advertising executive for Grapevine Concepts, has just launched a publicity campaign for a new restaurant in town, The Black Angus. Bill has just installed four billboards on a highway outside of town, and he knows from experience the probabilities that each will be noticed by a randomly chosen motorist. The probability of the first billboard's being noticed by a motorist is 0.75. The probability of the second's being noticed is 0.82, the third has a probability of 0.87 of being noticed, and the probability of the fourth sign's being noticed is 0.9. Assuming that the event that a motorist notices any particular billboard is independent of whether or not he notices the others, what is the probability that

(a) All four billboards will be noticed by a randomly chosen motorist?

(b) The first and fourth, but not the second and third billboards will be noticed?