Let's break this down. We're going to add 5921 and 5515 together.

Step 1: We'll start by adding the digits 1 & 5 in column 1 and get 6.

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

Step 3: We'll start by adding the digits 9 & 5 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 5 & 5 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 5921 + 5515 = 11436.

