A church hymn book contains 700 hymns, numbered 1 to 700. Each Sunday the congregation sings four different hymns. The numbers of the hymns are made known to the congregation by combining special small boards each containing a single digit. The board for 6 may be turned upside down to serve as a 9. What is the minimum number of small boards that are needed for showing any possible combination of four hymn numbers and how many of each number must there be?