Alright, let's solve this problem step by step. We have 1266 and 1099 and we're adding them together.

Step 1: We'll start by adding the digits 6 & 9 in column 1 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 6 & 9 in column 2 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 2 & 0 in column 3 and get 3.

Step 4: We'll start by adding the digits 1 & 1 in column 4 and get 2.

So, 1266 + 1099 = 2365.

