How many subsets of the set $\{1,2,3,4, 5, 6, 7, 8, 9, 10\}$ contain the number 5, 6, and 7?
Take 5,6, and 7
Now you can add 0 more, or 1 more or 2 more etc right up to all of them.
1 more 7C1 ways
2 more 7C2 ways
etc.
Now if you have any idea what I'm talking about you can finish it easily.