In a small town, a vampire and a werewolf are causing trouble. The vampire drains blood from 4 people each week, while the werewolf consumes 6 people each week, but only fresh ones, never those already drained by the vampire. If the town has 84 people, how many weeks will the town last before both the vampire and the werewolf run out of people? Let's think step by step and output the final answer within \boxed{}.
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