A student taking economics, statistics, and finance has decided to spend 9 hours per week studying. The objective is to maximize the average grade, which means maximizing the total grade in the three courses. The table shows the student's estimate of the relation between time spent studying each course and the grade for each course.

Hours of Study Economics Statistics Finance

0 50 42 56

1 62 54 68

2 71 64 76

3 79 72 82

4 85 80 87

5 88 84 90

6 90 87 93

7 92 89 95

Based on the above information, what is the maximum AVERAGE grade the student can earn if she studies 9 hours per week?

A. 80

B. 80.3

C. 82

D. 78.3

I need a detailed explanation of how to go about and get the 1. hours ratio and 2. the Avg grade