Let's break this down. We're going to add 3904 and 8030 together.

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

Step 2: We'll start by adding the digits 0 & 3 in column 2 and get 3.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 3 & 8 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 3904 + 8030 = 11934.

