First, let's draw a diagram showing how many people purchased each type of book:
Now, let's answer each question:
a)
only science: 12 customers
b)
mysteries and science, but not romance: 11 customers
c)
mysteries or science: 15+11+12+7+3+4 = 52 customers
d)
mysteries or science, but not romance: 15+11+12 = 38 customers
e)
exactly 2 types of books: 7+11+4 = 22 customers