Okay, we are tasked with adding 1104 and 3121. Let's begin!

Step 1: We'll start by adding the digits 4 & 1 in column 1 and get 5.

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 1 & 1 in column 3 and get 2.

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

So, 1104 + 3121 = 4225.

