Let's break this down. We're going to add 1020 and 3113 together.

Step 1: We'll start by adding the digits 0 & 3 in column 1 and get 3.

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

Step 3: We'll start by adding the digits 0 & 1 in column 3 and get 1.

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

So, 1020 + 3113 = 4133.

