Well your answer would be 24.
9 goes into 21, 2 times so you would get 18. You would take your 18 and subtract it from 21, you would get 3. Then you would bring down your remaining 6 and then see how many times 9 goes into 36. 9 goes into 36 4 times so you would get 24 as your answer.
To check your work you would multiply 24 by 9 and you would get 216.
HOPE THIS HELPS! ^_^
