OK, let's do this. We've got 135 and 707 and we're adding them all together.

Step 1: We'll start by adding the digits 5 & 7 in column 1 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 0 in column 2 and get 4.

Step 3: We'll start by adding the digits 1 & 7 in column 3 and get 8.

So, 135 + 707 = 842.

