Okay, we are tasked with adding 4115 and 520. Let's begin!

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 & 2 in column 2 and get 3.

Step 3: We'll start by adding the digits 1 & 5 in column 3 and get 6.

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

So, 4115 + 520 = 4635.

