Not to worry, we've got 311 and 639. Let's get to adding them!

Step 1: We'll start by adding the digits 1 & 9 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 1 & 3 in column 2 and get 5.

Step 3: We'll start by adding the digits 3 & 6 in column 3 and get 9.

So, 311 + 639 = 950.

