Okay, we are tasked with adding 2103 and 6645. Let's begin!

Step 1: We'll start by adding the digits 3 & 5 in column 1 and get 8.

Step 2: We'll start by adding the digits 0 & 4 in column 2 and get 4.

Step 3: We'll start by adding the digits 1 & 6 in column 3 and get 7.

Step 4: We'll start by adding the digits 2 & 6 in column 4 and get 8.

So, 2103 + 6645 = 8748.

