OK, let's do this. We've got 721 and 207 and we're adding them all together.

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

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

Step 3: We'll start by adding the digits 7 & 2 in column 3 and get 9.

So, 721 + 207 = 928.

