Let's dive into this subtraction. We'll start with 663996 and subtract 27062 from it.

Step 1: We'll start by subtracting the digit 2 and the borrow 0 from 6 in column 1 and get 4.
4 is the first digit of our result.

Step 2: We'll start by subtracting the digit 6 and the borrow 0 from 9 in column 2 and get 3.
3 is the next digit of our result.

Step 3: We'll start by subtracting the digit 0 and the borrow 0 from 9 in column 3 and get 9.
9 is the next digit of our result.

Step 4: We'll start by subtracting the digit 7 and the borrow 0 from 3 in column 4 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 5: We'll start by subtracting the digit 2 and the borrow 1 from 6 in column 5 and get 3.
3 is the next digit of our result.

Step 6: We'll start by subtracting the digit 0 and the borrow 0 from 6 in column 6 and get 6.
6 is the next digit of our result.

So, 663996 - 27062 = 636934.