OK, let's do this. We've got 1644 and 9963 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 & 6 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 6 & 9 in column 3 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 1 & 9 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 1644 + 9963 = 11607.

