A computer company advertises its computers in PC World, in PC Magazine, and on television. A survey of 720 customers finds that the numbers of customers who are familiar with the company's computers because of the different forms of advertising are as follows:
305, PC World
290, PC Magazine
120, PC World and PC Magazine
136, PC Magazine and television
110, PC World and television
86, all three sources
How many of the surveyed customers know about the computers because of:
(a) exactly one of these forms of advertising?
(b) exactly two of these forms of advertising?
(c) PC World and neither of the other two forms of advertising?