No problem, let's work through this together. We're starting with 1991 and 8881 and adding them all up.

Step 1: We'll start by adding the digits 1 & 1 in column 1 and get 2.

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 9 & 8 in column 3 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 1 & 8 in column 4 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 1991 + 8881 = 10872.

