We have numbers 3015 and 6521. Let's start adding them together.

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

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 0 & 5 in column 3 and get 5.

Step 4: We'll start by adding the digits 3 & 6 in column 4 and get 9.

So, 3015 + 6521 = 9536.

