Okay, we are tasked with adding 612 and 129. Let's begin!

Step 1: We'll start by adding the digits 2 & 9 in column 1 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 1 & 2 in column 2 and get 4.

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

So, 612 + 129 = 741.

