Suppose that a certain college class contains 43 students. Of these, 28 are seniors, 22 are physics majors, and 10 are neither. A student is selected at random from the class.
(a) What is the probability that the student is both a senior and a physics major?

(b) Given that the student selected is a physics major, what is the probability that he is also a senior?
Write your responses as fractions.