10. Calculate in how many ways each of the following choices can be made: a. 4 books are to be chosen from a list of 9 titles to take away for reading during a holiday, b. 15 people have sent in winning entries for a magazine competition, and three are to be chosen and placed in order of merit so as to receive the 1st, 2nd, and 3rd prizes. c. A committee of 3 people comprising the president, secretary, and treasurer are to be chosen from 8 possible candidates