No problem, let's work through this together. We're starting with 3399 and 5480 and adding them all up.

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

Step 2: We'll start by adding the digits 9 & 8 in column 2 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 3 & 4 in column 3 and get 8.

Step 4: We'll start by adding the digits 3 & 5 in column 4 and get 8.

So, 3399 + 5480 = 8879.

