For the given configuration, determine how many different license plates are possible if (a) digits and letters can be repeated, and (b) digits and letters cannot be repeated 4 letters followed by 3 digits
a) (26^4) * (10^3) = 456,976,000
b) (26 * 25 * 24 * 23) * (10 * 9 * 8 ) = 258,336,000
