Not to worry, we've got 6559 and 1421. Let's get to adding them!

Step 1: We'll start by adding the digits 9 & 1 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 2 in column 2 and get 8.

Step 3: We'll start by adding the digits 5 & 4 in column 3 and get 9.

Step 4: We'll start by adding the digits 6 & 1 in column 4 and get 7.

So, 6559 + 1421 = 7980.

