Let's get this math done. We have 9921 and 4931 and we're going to add them all together.

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 2 & 3 in column 2 and get 5.

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

So, 9921 + 4931 = 14852.

