Okay, we are tasked with adding 4201 and 3405. Let's begin!

Step 1: We'll start by adding the digits 1 & 5 in column 1 and get 6.

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

Step 3: We'll start by adding the digits 2 & 4 in column 3 and get 6.

Step 4: We'll start by adding the digits 4 & 3 in column 4 and get 7.

So, 4201 + 3405 = 7606.

