Let's break this down. We're going to add 8420 and 323 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 & 2 in column 2 and get 4.

Step 3: We'll start by adding the digits 4 & 3 in column 3 and get 7.

Step 4: We'll start by adding the digits 8 & 0 in column 4 and get 8.

So, 8420 + 323 = 8743.

