At a certain university, 30% of the students major in math. Of the students majoring in math, 60% are males. Of all the students at the university, 70% are males.
a) What is the probability that a student selected at random in the university is male and majors in math?
b) What is the probability that a randomly selected student in the university is female or majors in math or both?
I got a) as 18%, I am not sure how to do b).