We've got two numbers: 6601 and 6380. Let's find their sum.

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

Step 2: We'll start by adding the digits 0 & 8 in column 2 and get 8.

Step 3: We'll start by adding the digits 6 & 3 in column 3 and get 9.

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, 6601 + 6380 = 12981.

