The Reverse Numbers

Let’s try the following steps:
* Write the number with 2 digits.
* Reverse that number.
* Find the difference between that 2 numbers from step 1 and step 2
* Divide the answer from step 3 by the positive difference between 2 digits number from step 1.
* The result absolutely always 9. Why??
Example:

step 1	97	81	12
step 2	79	18	21
step 3	|97 – 79| = 18	|81 – 18| = 63	|12 – 21| = 9
step 4	18 : |9-7| = 9	63 : |8-1| = 9	9 : |1-2| = 9