The correct answer to this question is D, 9 x 9 x 8 x 7 x 6. Being that the first digit isn't 0, the first position has 9 possible choices. The second position allows 0, which allows for 9 possible choices as well. From there, the third allows eight, the fourth allows 7, and the fift allows 6 possible choices.
This algebra question can be solved by reasoning, as well as using the permutation formular. This formula lists objects in order of importance. It is used when counting with the order matters and when it can be counted without replacements.