When carrying out a survey on the popularity of three different brands X, Y and Z of washing powder, 100 users were interviewed, and the results were as follows: 30 used brand X only, 22 used brand Y only, 18 used brand Z only, 8 used brands X and Y, 9 used brands X and Z, 7 used brands Z and Y and 14 used none of the brands.

(a) How many users used brands X, Y and Z?

(b) How many users used brands X and Z but not brand Y?