Okay, we are given 6427 and 6215. Let's add them up step by step.

Step 1: We'll start by adding the digits 7 & 5 in column 1 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 2 & 1 in column 2 and get 4.

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

Step 4: We'll start by adding the digits 6 & 6 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 6427 + 6215 = 12642.

