So you have
8 digits (number available) to form
3 digit numbers (number selected).
Using the formula

where a is the number of available digits, P is the permutation function and c is the number of digits to be selected.
The number of three digit numbers that can be formed =

=
336 O R
By using the formula
where a is the number of available digits and c is the number of digits to be selected.
⇒

⇒

⇒ Permutation = 336