Answer:
The number of possible combinations is 180
Step-by-step explanation:
The numbers to select from are 3-8
These are 6 numbers 
Now, the restriction we have is that the 3 characters cannot be the same 
For the first character, we have 6 choices;
For the second character, we have another 6 choices 
For the last character, since it cannot be the same, we can only have 5 choices 
So the possible number of choices will be;
6 * 6 * 5 = 189 combinations