In the mid-1980s, the state of Florida ran out of combinations of letters and numbers for its license plates. Then, each license plate contained three letters of the alphabet, followed by three digits selected from the 10 digits 0, 1, 2, . , 9.
a. How many different license plates did this system allow?
b. New Florida tags were obtained by reversing the procedure, starting with three digits followed by three letters. How many new tags did the new system provide?
c. Since the new tag numbers were added to the old numbers, what is the total number of licenses available for registration in Florida?