Each day, workers at the Gotham City Police Department work two 6hr shifts chosen from, 12am-6am, 6am-12pm, 12pm-6pm, and 6pm-12am. The following number of workers are needed during each shift: 12am-6am (15 workers), 6am-12pm (5 workers), 12pm-6pm (12 workers), and 6pm-12am (6 workers). Workers whose two shifts are consecutive are paid $12/hr; workers whose shifts are not consecutive are paid $18/hr. Formulate an LP (linear programming problem) that can be used to minimize the cost of meeting the daily workforce demands of the Gotham City Police Department.