math for 10 years old that 38 years old cant do

 72    99    27    45    18    39    21    28    13    21    ?

What is the ? and please read the rest and use your tactic on all of the numbers

  

This question is for smart kids but if you think you know the answer see the second last numbers and try that with your thinking if you think you know the answer scroll down.

To be honest I think a 10 year old can actually solve this quicker than a adult if your kid can do this question faster than your parent your intelligent.

                                                         answer   7

you plus 72 with 27 you get 99 right but in this case you take 72s 2 and plus it with 27s 7 so you get 9 and 9 and it works with the second last one try it yourself

If you have any question feel free to write it in the comment