We've got two numbers: 403 and 872. Let's find their sum.

Step 1: We'll start by adding the digits 3 & 2 in column 1 and get 5.

Step 2: We'll start by adding the digits 0 & 7 in column 2 and get 7.

Step 3: We'll start by adding the digits 4 & 8 in column 3 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 403 + 872 = 1275.

