Professor Smith teaches two sections of business statistics, which together will be graded with 120 final exams. Professor Smith has two graduate assistants, Brad and Sarah, who will be taking final exams. There are 3 days between the start of the test and when final grades must be released. During this period, Brad has 12 hours of free time and Sarah has 10 hours to grade the exam. Brad took an average of 7.2 minutes to grade the exam and Sarah 12 minutes; however, Brad's exam would have errors, requiring Professor Smith to eventually re-score 10% of the exam, compared to only 6% Sarah's exam needs to be remarked. Professor Smith wanted to know how many exams each graduating automotive assistant would be assigned to grade in order to minimize the number of exams to be remarked. 

a. Develop a linear programming model for this problem. 

b. Solve this model using graphical analysis