We've got two numbers: 9599 and 2659. Let's find their sum.

Step 1: We'll start by adding the digits 9 & 9 in column 1 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 9 & 5 in column 2 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 5 & 6 in column 3 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 9 & 2 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 9599 + 2659 = 12258.

