Write a method that accepts a string of nothing but numeric digits. The string will have at least one character (no empty strings). The first character will indicate which digit to perform a "checksum" on. If the first digit is a "3" return the number of 3's that appear in the string EXCLUDING that first "3". If the first digit is a "7" return the number of 7's that appear in the string EXCLUDING that first "7". Look at the test data for examples.