Let's break this down. We're going to add 3993 and 8503 together.

Step 1: We'll start by adding the digits 3 & 3 in column 1 and get 6.

Step 2: We'll start by adding the digits 9 & 0 in column 2 and get 9.

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 3 & 8 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 3993 + 8503 = 12496.

