What is the difference between the largest and smallest natural three-digit numbers, all of which are different?

The largest three-digit number is 999. But it has duplicate digits. To find the largest natural three-digit number for which all digits are different, we will decrease the digits in the tens and ones digits. The smallest three-digit number is 111, but it has duplicate digits. To find the smallest natural three-digit number that does not have duplicate digits, we increase the digits in the tens and ones ranks. We’ll get 123.
987-123 = 864
As you can see, the first answer.
Answer: 864.