Okay, we are tasked with adding 15 and 817. Let's begin!

Step 1: We'll start by adding the digits 5 & 7 in column 1 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

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

Step 3: We'll start by adding the digits 0 & 8 in column 3 and get 8.

So, 15 + 817 = 832.

