There are 336,000 different combinations that can be made.
Step-by-step explanation
The first 3 letters and can not repeat, and are from the first 8 letters of the alphabet. We can multiply 8*7*6 because no letter will be the same as the others.
The numbers can be repeated, and have 10 possible outcomes 3 times. Therefore, we can add 10*10*10 to our equation.
At this point, we have 10*10*10*8*7*6, which comes out to be 336,000.