Let's solve this addition problem. We have 1155 and 109, and we need to add them together.

Step 1: We'll start by adding the digits 5 & 9 in column 1 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 6.

Step 3: We'll start by adding the digits 1 & 1 in column 3 and get 2.

Step 4: We'll start by adding the digits 1 & 0 in column 4 and get 1.

So, 1155 + 109 = 1264.

