2 Each day, Sunco manufactures four types of gasoline:

lead-free premium (LFP), lead-free regular (LFR), leaded premium (LP), and leaded regular (LR). Because of cleaning and resetting of machinery, the time required to produce a batch of gasoline depends on the type of gasoline last produced. For example, it takes longer to switch between a lead-free gasoline and a leaded gasoline than it does to switch between two lead-free gasolines. The time (in minutes) required to manufacture each day’s gasoline requirements are shown in Table 75. Use a branch-andbound approach to determine the order in which the gasolines should be produced each day.

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TABLE 75 Last-Produced Gas to Be Next Produced Gasoline LFR LFP LR LP LFR 50 120 LFP 60 140 110 LR 90 130 LP 130 120 80 140 60 Note: Assume that the last gas produced yesterday precedes the first gas produced today.