Okay, we are tasked with adding 1343 and 8421. 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 4 & 2 in column 2 and get 6.

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

Step 4: We'll start by adding the digits 1 & 8 in column 4 and get 9.

So, 1343 + 8421 = 9764.

