At a meeting of
![12k](/media/m/d/4/8/d4848c7f56eaf6de6b146fa1cdd0e355.png)
people, each person exchanges greetings with exactly
![3k+6](/media/m/a/9/c/a9ce05d66ebaf41f4b285e379317756c.png)
others. For any two people, the number who exchange greetings with both is the same. How many people are at the meeting?
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At a meeting of $12k$ people, each person exchanges greetings with exactly $3k+6$ others. For any two people, the number who exchange greetings with both is the same. How many people are at the meeting?