OK, let's do this. We've got 6400 and 3569 and we're adding them all together.

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

Step 2: We'll start by adding the digits 0 & 6 in column 2 and get 6.

Step 3: We'll start by adding the digits 4 & 5 in column 3 and get 9.

Step 4: We'll start by adding the digits 6 & 3 in column 4 and get 9.

So, 6400 + 3569 = 9969.

