Hi
You need to carry over the 1 in 11 in your answer.
Here are the steps:
736 + 255 = _ _ _
Adding 7 +2 we get 9. So 9 becomes the first digit of the answer.
736 + 255 = 9Â _ _
Adding 3 +5 we get 8. And 8 becomes the first digit of the answer.
736 + 255 = 9 8Â _
Adding 6 +5 we get 11. Since 11 has two digits, we carry over the first 1 in 11. So the answer 98 becomes 99.
736 + 255 = 9 9Â _
The second 1 in 11 becomes the third digit of the answer.
736 + 255 = 9 9Â 1
Hope this clarifies.