You want to have 3 different letters at first, in the first "slot" for a letter, there are 26 letters to choose from. Next slot there is only 25, because one is taken. Last slot there is 24. Then for the numbers, we can use the same technique. In the first "slot" there are 10 digits to choose from. In the second there are 9. Now we get to multiply them up: 26*25*24*10*9=14,040,000
