We've got two numbers: 2001 and 8408. Let's find their sum.

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

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 0 & 4 in column 3 and get 4.

Step 4: We'll start by adding the digits 2 & 8 in column 4 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 2001 + 8408 = 10409.

