OK, let's do this. We've got 66 and 407 and we're adding them all together.

Step 1: We'll start by adding the digits 6 & 7 in column 1 and get 13.
We'll write down the last digit 3 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 & 4 in column 3 and get 4.

So, 66 + 407 = 473.

