Question 148291
In this particular question, the different ways of possible players that a coach can choose from the 1st, 2nd, and 3rd batter. Therefore, using The Rule of Sum we can solve. 

For the 1st player he has 15 different ways to choose from
For the 2nd player he has 14 different ways to choose from
For the 3rd player he has 13 different ways to choose from

Therefore, 

For the first experiment or the second or the last is 15 + 14 + 13 = 42 possible ways the coach can choose the 1st, 2nd, and 3rd batters.