• 15 drivers are required for the Friday night shift.

• 12 drivers are required for the Saturday morning shift.

• 9 drivers are required for the Sunday morning shift.

Given that every driver must work on at least one of these shifts, what is the maximum number of drivers that can work on all three shifts?

Notice that there are 15 + 12 + 9 = 36 shifts total. How many of those shifts are taken up by the drivers that work all 3? How many shifts are remaining for the other 21-n drivers? Can you write an equation or inequality now using the restriction that every driver needs to work on at least one shift?

Hope this helped, and let me know if you have questions!

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