We have 100 letters: 81-$M$, 10-$B$, 7-$S$ , 2-$H$. How many ways we can choose 4 letters so we can write : $SBBH$

Question

I'm struggling with this question and here's what I did:
for example the $S$ letter, we need just one, so what I thought about is doing $100 \choose 7$$7 \choose 1$. (choosing the $7$ letters $S$ then choosing one from them). and it goes like that for the rest of the letters then I add the results up.
I feel like I'm making mistakes and I'm not sure of my solution, would appreciate any feedback and tips.

Answer 1

You need an S $7 \choose 1$, two B $10 \choose 2$ and one H $2 \choose 1$.