Okay, we are tasked with adding 105 and 5420. Let's begin!

Step 1: We'll start by adding the digits 5 & 0 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 & 4 in column 3 and get 5.

Step 4: We'll start by adding the digits 0 & 5 in column 4 and get 5.

So, 105 + 5420 = 5525.

