Let's break this down. We're going to add 6801 and 4100 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 0 & 0 in column 2 and get 0.

Step 3: We'll start by adding the digits 8 & 1 in column 3 and get 9.

Step 4: We'll start by adding the digits 6 & 4 in column 4 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 6801 + 4100 = 10901.

