The sum of the equation 9+10 is equal to 19. One way to think about this problem might have been to use shapes to represent each number. You might have drawn 9 circles and 10 triangles. Then, count the total number of shapes that you have drawn on your paper and discover that there are 19 total shapes.
If you are having a more difficult time adding numbers, it might be a good idea to break down these numbers into smaller pieces. The number 10 can be be broken down into 2 sets of 5. The number 9 can be broken down into a set of 5 and a set of 4. Then you can count all of your different sets. Counting your sets, you will notice that you add 5+5=10, 10+5=15, and 15+4=19.
There are many excellent ways to find the correct sum.