Answer the following: a) How many license plates can be made using either three digits followed by three uppercase English letters or three uppercase English letters followed by three digits? b) How many license plates can be made using either three uppercase English letters followed by three digits or four uppercase English letters followed by two digits? c) How many bit strings of length seven either begin with two Os or end with three 1s? d) How many bit strings of length 10 contain either five consecutive Os or five consecutive 1s