13. (12pts) In a particular state, the license plates have 7 characters. Each character can letter or a digit (0,1,2,....9). How many different license plates be an upper case can there be if (a) There is no restriction. (b) The license plates must start with a digit. (c) The license plates must start with a "0" or end with a "0" (d) The license plates must contain at least one "0. (e) No character appears more than once on the same license plate. (f) Exactly 3 of the 7 characters are digits