OK, let's do this. We've got 9924 and 6534 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 4 in column 1 and get 8.

Step 2: We'll start by adding the digits 2 & 3 in column 2 and get 5.

Step 3: We'll start by adding the digits 9 & 5 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 9 & 6 in column 4 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

So, 9924 + 6534 = 16458.

