A study was done to determine the efficacy of three different drugs—A, B, and C—in relieving headache pain. Over the period covered by the study, 50 subjects were given the chance to use all three drugs. The following results were obtained:

21 reported relief from drug A
21 reported relief from drug B
31 reported relief from drug C
6 reported relief from both A and B
14 reported relief from both drugs A and C.
15 reported relief from both drugs B and C.
41 reported relief from at least one of the drugs.

Required:
a. How many people got relief from none of the drugs?
b. How many people got relief from all three drugs?
c. How many subjects got relief from A only?