Let's solve this addition problem. We have 4123 and 9881, and we need to add them together.

Step 1: We'll start by adding the digits 3 & 1 in column 1 and get 4.

Step 2: We'll start by adding the digits 2 & 8 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 1 & 8 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

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

So, 4123 + 9881 = 14004.

