Which of these numbers are exactly divisible by 9? 107,513,944,126,80

513 and 126 both are. (The question doesn't say
that there's only one of them in the list.)

Here's an easy way to tell:  (I don't know how or why it works,
but it works.)

You're looking at a big number, and you need to find out if it's
divisible by 9.
Here's the two-step process:
-- If it's going to be divisible by 9, then it has to be divisible by 3.
-- Find out whether it's divisible by 3.  If it is, then ...
-- Find out whether it's divisible by 9.

Step 1:
Add up all the digits in the number. If that sum is divisible by 3,
then the original big number is too.

Example:
Is 549 divisible by 3  ?
Add up its digits:  (5 + 4 + 9) = 18 .
Is 18 divisible by 3 ?
Yes.  That tells you that 549 is divisible by 3 .
So it could be divisible by 9.

Step 2:
Take that same  18  and add up its digits.
(1 + 8) = 9.
9 is divisible by 3.
This tells you that the original big number ... 549 ... is also divisible by 9 .