Okay, we are tasked with adding 120 and 6459. Let's begin!

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

Step 2: We'll start by adding the digits 2 & 5 in column 2 and get 7.

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 & 6 in column 4 and get 6.

So, 120 + 6459 = 6579.

