23. Suppose that an instructor uses four grades to determine a student's course average: a quiz. an assignment, a mid-trim exam and a final exam. These are weighted as 5%, 15%, 25% and 60%, respectively. If a student's scores are 70%, 80%, 60%, and 90%, respectively, compute the student's course average. a) 73.7 b) 77.1 c) 77.3 d) 83