If numbers cannot be repeated :
8 * 7 * 6
If numbers can be repeated :
8 * 8 * 8
The logic is that we have 8 different possibilities for the first digit. Then each of those 8 possibilities have 8 (or 7 if no repeats) for the second digit. Then each of those possibilites have 8(or 6 if no repeats) for the third digit.