(20 points) Solve the following two " union " type questions: (a) How many bit strings of length 7 either begin with 3 0s or end with 1 1s? (inclusive or) (b) Every student in a discrete math class is either a computer science or a mathematics major or is a joint major in these two subjects. How many students are in the class if there are 40 computer science majors (including joint majors), 20 math majors (including joint majors) and 6 joint majors?