Moodle课程总成绩计算

I created a course in Moodle and a quiz in it. The quiz consists of 34 questions and the number of quiz total correct answers is stored in $quiz I want to calculate the Course Total Grade according to the following function :

function getfinalgrade($quiz)
{
    switch($quiz)
    {
Case 1  : $fg = 74  ; break;
Case 2  : $fg = 74  ; break;
Case 3  : $fg = 74  ; break;
Case 4  : $fg = 77  ; break;
Case 5  : $fg = 80  ; break;
Case 6  : $fg = 83  ; break;
Case 7  : $fg = 86  ; break;
Case 8  : $fg = 89  ; break;
Case 9  : $fg = 92  ; break;
Case 10 : $fg = 95  ; break;
Case 11 : $fg = 98  ; break;
Case 12 : $fg = 102 ; break;
Case 13 : $fg = 105 ; break;
Case 14 : $fg = 109 ; break;
Case 15 : $fg = 113 ; break;
Case 16 : $fg = 116 ; break;
Case 17 : $fg = 120 ; break;
Case 18 : $fg = 123 ; break;
Case 19 : $fg = 127 ; break;
Case 20 : $fg = 130 ; break;
Case 21 : $fg = 134 ; break;
Case 22 : $fg = 138 ; break;
Case 23 : $fg = 141 ; break;
Case 24 : $fg = 145 ; break;
Case 25 : $fg = 148 ; break;
Case 26 : $fg = 152 ; break;
Case 27 : $fg = 156 ; break;
Case 28 : $fg = 159 ; break;
Case 29 : $fg = 163 ; break;
Case 30 : $fg = 166 ; break;
Case 31 : $fg = 169 ; break;
Case 32 : $fg = 172 ; break;
Case 33 : $fg = 175 ; break;
Case 34 : $fg = 177 ; break;
  }
return($fg);
}

Does anybody know how to implement this ???

Thank you

There could me more than 14 grade letters, it is just a little bit unclear how to add them: You just have to fill your three lowest empty fields with correct values and then three more appear after save. Check the bug tracker report for info: https://tracker.moodle.org/browse/MDL-51879