Answer:
.
Explanation:
Hopefully this will help. Let me know in the comments if it doesn't.
The domain is all the x's where the function exists. The function you have starts at x=3 and ends at x=7. There are no breaks in your line between those numbers for x. So your domain is all x's between 3 and 7 ( inclusive).
So that means all values of x that is greater than or equal to 3 and values of x less than or equal to 7.
.