Okay, we are tasked with adding 1203 and 671. Let's begin!

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

Step 2: We'll start by adding the digits 0 & 7 in column 2 and get 7.

Step 3: We'll start by adding the digits 2 & 6 in column 3 and get 8.

Step 4: We'll start by adding the digits 1 & 0 in column 4 and get 1.

So, 1203 + 671 = 1874.

