Okay, we are tasked with adding 4173 and 4221. 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 7 & 2 in column 2 and get 9.

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

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

So, 4173 + 4221 = 8394.

