Permutations with repetition and choice

How does the permutation formula look if you’re choosing numbers and there’s also repeats.
For example, for this question:

If I was trying to solve using the formula

Which formula exactly? I would just use the multiplication principle - in how many ways can the first digit of the number be filled? What about the second and third?

n!/(n-r)!

I just wanted to understand it from another angle

That’s not really how I’d do it. Think about the multiplication principle - this is easier that you probably think.

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