Alright, let's solve this problem step by step. We have 1991 and 5500 and we're adding them together.

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 9 & 0 in column 2 and get 9.

Step 3: We'll start by adding the digits 9 & 5 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 1 & 5 in column 4 and get 7.

So, 1991 + 5500 = 7491.

