Intersection and conditional probability: Can anyone help me with a breakdown of this question?

V Suppose that a certain college class contains 65 students. Of these, 30 are seniors, 39 are physics majors, and 6 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. (If necessary, consult a list of formulas.) (b)