Answer 1

Combination without repetition:
n! / (k!(n-k)!
25!/ (7! * 18!) = 480700 possible ways.
It's "maybe" the right answer, I wasn't too good in this jejeje.

Answer 2

can we put multiple balls in one hole?

Answer 3

cnp(25,7) https://code.sololearn.com/czAFSwbs9SAE/?ref=app