Let's break this down. We're going to add 4502 and 7521 together.

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

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

Step 3: We'll start by adding the digits 5 & 5 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 4 & 7 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 4502 + 7521 = 12023.

