OK, let's do this. We've got 6411 and 3357 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 1 & 5 in column 2 and get 6.

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

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

So, 6411 + 3357 = 9768.

