Let's break this down. We're going to add 9318 and 9721 together.

Step 1: We'll start by adding the digits 8 & 1 in column 1 and get 9.

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

Step 3: We'll start by adding the digits 3 & 7 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 9 & 9 in column 4 and get 19.
We'll write down the last digit 9 and carry the 1 to the next column.

So, 9318 + 9721 = 19039.

