We have numbers 68 and 709. Let's start adding them together.

Step 1: We'll start by adding the digits 8 & 9 in column 1 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 6 & 0 in column 2 and get 7.

Step 3: We'll start by adding the digits 0 & 7 in column 3 and get 7.

So, 68 + 709 = 777.

