Let's break this down. We're going to add 604 and 2251 together.

Step 1: We'll start by adding the digits 4 & 1 in column 1 and get 5.

Step 2: We'll start by adding the digits 0 & 5 in column 2 and get 5.

Step 3: We'll start by adding the digits 6 & 2 in column 3 and get 8.

Step 4: We'll start by adding the digits 0 & 2 in column 4 and get 2.

So, 604 + 2251 = 2855.

