OK, let's do this. We've got 5355 and 1002 and we're adding them all together.

Step 1: We'll start by adding the digits 5 & 2 in column 1 and get 7.

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 5.

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

Step 4: We'll start by adding the digits 5 & 1 in column 4 and get 6.

So, 5355 + 1002 = 6357.

