Okay, we are tasked with adding 5591 and 5687. Let's begin!

Step 1: We'll start by adding the digits 1 & 7 in column 1 and get 8.

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 5 & 6 in column 3 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 5 & 5 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 5591 + 5687 = 11278.

