Okay, we are tasked with adding 503 and 296. Let's begin!

Step 1: We'll start by adding the digits 3 & 6 in column 1 and get 9.

Step 2: We'll start by adding the digits 0 & 9 in column 2 and get 9.

Step 3: We'll start by adding the digits 5 & 2 in column 3 and get 7.

So, 503 + 296 = 799.

