The sixth-grade experimental class has a large mathematical difficulty coefficient in improving the test paper. According to the relevant public information, it is found that it is difficult for the top students in the sixth grade experimental class to design math test questions, and the difficulty coefficient reflects the difficulty of the test questions, that is, the degree to which candidates lose points in a test question or a test paper. If the full mark is 150, the average score of candidates is 108 and the average score is 42, then the difficulty coefficient is 108/ 150=0.72.