The DT Tape Recorder Company manufactures three models which have revenue contributions of $55, $90, and $120, for Models A, B, and C, respectively. Production costs for the three models are $40, $55, and $74 for Models A, B, and C, respectively. The weekly minimum production requirements are 25 for Model A, 130 for Model B, and 55 for Model C. Each type of recorder requires a certain amount of time for the manufacturing of component parts, for assembling, and for packaging. Specifically, a dozen units of Model A require four hours for manufacturing, three hours for assembling, and one hour for packaging. The corresponding figures for a dozen units of Model B are 2.5, 4, and 2, and for a dozen units of Model C are 6, 9, and 4. During the forthcoming week, the company has available 130 hours of manufacturing, 170 hours of assembling, and 3,120 minutes of packaging time. Formulate this problem as a linear programming model for scheduling production for the upcoming week.