Solve the problem. How many possible selections are there

Solve the problem.
* When you come across a question like this, what is the first thing you look at to help you proceed with solving the problem? Please explain to me the steps.

The library is to be given 3 books as a gift. The books will be selected from a list of 18 titles. If each book selected must have a different title, how many possible selections are there?
A) 816
B) 6.402373706e+15
C) 4896
D) 1.067062284e+15

The first answer is right. The way you get those numbers is like this:

There are 18 titles to choose from, so there are 18 choices for the first book. The books all have to be different, so the second book can be anything other than the first book, so there are 17 choices (all 18 of the original titles minus the 1 title chosen for the first book). Similarly, the third book can be anything other than the first or second book, so there are 16 choices (the 18 titles minus the 2 titles of the first two books). Thus, the total number of choices is 18*17*16, or 4896, so answer C is right.

Hope that helps :)

1st book ..........18 choices
2nd book..........17 choices
3rd book ........16 choices
so for all three books =18x17x16=4896