Answer:
18a+9
Explanation:
(If confused please tell me)
When a question like this comes up, you have to multiply the outside number (which is currently 9) and the two numbers inside the parentheses. First you multiply 9x2a, which is 18 but you must not forget the letter so in that case it will be 18a. Now you have to do 9x1 which is 9, there is no letter so in that case you just leave it. There is still a + sign but you can't add them b/c they're differ, one has a letter and the other doesn't. In that case you just leave it like, 18a+9.