Suppose 6 students (Bob, Carlos, Dave, Xing, Yolanda, and Zori) are planning to study together for 5 classes (APM346, ENV200, MAT235, PHL245, and STA355). They want to choose times so that everyone in a class can attend, and they will only discuss one class during that time. Not every student is in every class: B, D, X, Y are in APM346. C, Y are in ENV200. B, Y, Z are in MAT235. B, D, Z are in PHL245. C, X are in STA355. . . . Draw a graph whose vertices represent the courses, with an edge between two courses that cannot be scheduled together. What is the minimum number of time slots they will need