Hm, ok. Here's how best to tackle this question - let's look at OPTIONS!
We have three spots to fill, spots A, B, & C.
For spot A, there are 7 different options for what location will fill that spot.
Regardless of which location is selected, that means that now there are only 6 options left for which location will fill spot B.
Finally, it doesn't matter which locations fill spots A and B, there will be 5 options left to fill spot C.
In the end, we need to multiply together the number of options for spots A, B, and C.
7 * 6 * 5 = 210