Answer:
ab
Explanation:
When all of the variables are the same in a problem, think of them as the same term. They can be added and subtracted just as you would add and subtract normal numbers.
For example if I have 5 bananas on a table and take away 3 bananas. I only have two bananas left (2b). It's the same when there are variables!
Subtract 9 from 3:
-6ab+7ab
Add -6 to 7:
ab
Your final answer is ab!