Let's break this down. We're going to add 2604 and 351 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 & 3 in column 3 and get 9.

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

So, 2604 + 351 = 2955.

