Three-set Venn Diagram Problem 02

Try this one on your own...
In a college mathematics class, all students are also taking anthropology, history or psychology, and some of the students are taking two, or even all three of these courses. Suppose

45 students are taking anthropology,
45 students are taking history,
40 students are taking psychology,
4 students are taking all three courses,
15 students are taking anthropology and history,
20 students are taking psychology and anthropology.

a. How many students are taking only anthropology?
b. How many students are taking anthropology or history?
c. How many students are taking anthropology and history, but not psychology?

Ans: a. 14, b. 75, c. 11