The formula used is
course grade = 0.75 x exams grade + 0.25 x homework grade
The threshhold for a grade of n is (n-1).85; the threshhold for an `n-' grade is (n-1).6; the threshhold for a `+' grade is n.2. So, for example, if your weighted average from the above formula is between 2.6 and 2.84, your course grade is B-; if the average is between 2.85 and 3.19, your course grade is B; if the average is between 3.2 and 3.59, your grade is B+.