Alright, let's solve this problem step by step. We have 5559 and 2169 and we're adding them together.

Step 1: We'll start by adding the digits 9 & 9 in column 1 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 6 in column 2 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 5 & 1 in column 3 and get 7.

Step 4: We'll start by adding the digits 5 & 2 in column 4 and get 7.

So, 5559 + 2169 = 7728.

