A school vending machine sells cartons of milk and juice. On a typical day: No cartons are sold between 7 A. M. and 8 A. M., or from 5 P. M. onward The machine has a capacity of 100 cartons. At 7 A. M. it is three-quarters full. From 8 A. M. to 10 A. M., 10:15 A. M. to noon, and from 1 P. M. to 3 P. M. the students are in class. Students are NOT allowed to use the vending machines during class time. The machine is filled at 11 A. M. and at 4 P. M. Sketch a graph of the number of cartons in the vending machine as a function of time.