Let's break this down. We're going to add 405 and 7412 together.

Step 1: We'll start by adding the digits 5 & 2 in column 1 and get 7.

Step 2: We'll start by adding the digits 0 & 1 in column 2 and get 1.

Step 3: We'll start by adding the digits 4 & 4 in column 3 and get 8.

Step 4: We'll start by adding the digits 0 & 7 in column 4 and get 7.

So, 405 + 7412 = 7817.

