Can you explain to me how to do parts a and b?

12. An algebra teacher is writing a 90-minute test. There will be two types of questions: multiple choice and open-ended. The multiple-choice questions each take 3 minutes to complete, and the open- ended questions each take 12 minutes to complete. There must be at least 3 open-ended questions, at least 10 multiple-choice questions, and the test should take no more than 84 minutes. a. Write this scenario as a system of inequalities, using M for the number of multiple choice problems and O for the number of open-ended problems. louie al b. Graph the system of inequalities that you found in part (a). Put M on the horizontal axis and O on the vertical axis