Impasta

Let's use constructive counting to find the answer. There are 6 choices for the first letter, then 5, and so on. For the numbers, there are 10 choices for the first number, and 9 for the second. Since these choices are independent of each other, we can multiply these numbers together. Does my explanation make sense?

Is this from a class or from the book?

How do you know which problems come from AoPS?

No, I'm assuming it might have come from Introduction to Pre-Algebra or whatever it's called, given the depth of AoPS courses.

Out of curiousity, which class did these problems come from?