2. a)For the first letter in the license plate, it can be one of 24 letters since there are 26 letters in the English alphabet and I and O cannot be chosen. Same for the 3 next letters. The first digit can be one of 9, the second and the lasts can be one of out 10. Therefore the result is $24^3*9*10^3=124,416,000$.
b) $124,416,000-3,000,000=121,416,000$