<h3> </h3><h2> F-{1} (x)= x/6 + 5/6</h2>
The answer to your problem is a+6x+5.
Pretty sure it’s D but if it is not then I don’t know
There's 9 choices for the first digit and 4 choices for the last digit. The number of choices for the 2nd and 3rd digits is 90 if 2 numbers are different. or 100 if duplicates are allowed.
If duplicates are allowed the answer is 9 * 100 * 4 = 3600 possible numbers.
