Let's break this down. We're going to add 2635 and 2120 together.

Step 1: We'll start by adding the digits 5 & 0 in column 1 and get 5.

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

Step 3: We'll start by adding the digits 6 & 1 in column 3 and get 7.

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

So, 2635 + 2120 = 4755.

