19
10 - (-9) = 19
18
When you add -9 and +10, you get (+) 1.
19
add 9 plus 5 than subtract 1 from 5 to add it to 9 will give you 10
-1
19
10
you add 9 and 10. then you get 19 you divide by 2 and that's how you get your answer.=)
If you add 9+10 you would got 19
Add one mate.
10 and 8