Let's break this down. We're going to add 1515 and 7200 together.

Step 1: We'll start by adding the digits 5 & 0 in column 1 and get 5.

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

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

Step 4: We'll start by adding the digits 1 & 7 in column 4 and get 8.

So, 1515 + 7200 = 8715.

