We've got two numbers: 3918 and 9720. Let's find their sum.

Step 1: We'll start by adding the digits 8 & 0 in column 1 and get 8.

Step 2: We'll start by adding the digits 1 & 2 in column 2 and get 3.

Step 3: We'll start by adding the digits 9 & 7 in column 3 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 3 & 9 in column 4 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

So, 3918 + 9720 = 13638.

