We have numbers 3630 and 15. Let's start adding them together.

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

Step 2: We'll start by adding the digits 3 & 1 in column 2 and get 4.

Step 3: We'll start by adding the digits 6 & 0 in column 3 and get 6.

Step 4: We'll start by adding the digits 3 & 0 in column 4 and get 3.

So, 3630 + 15 = 3645.

