Let's solve this addition problem. We have 20 and 819, and we need to add them together.

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

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

Step 3: We'll start by adding the digits 0 & 8 in column 3 and get 8.

So, 20 + 819 = 839.

