OK, let's do this. We've got 644 and 303 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 3 in column 1 and get 7.

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

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

So, 644 + 303 = 947.

