OK, let's do this. We've got 4421 and 3903 and we're adding them all together.

Step 1: We'll start by adding the digits 1 & 3 in column 1 and get 4.

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

Step 3: We'll start by adding the digits 4 & 9 in column 3 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 4 & 3 in column 4 and get 8.

So, 4421 + 3903 = 8324.

