Good Riddles

Question: 8,549,176,320 What makes this number unique?

Question: 7 months have 31 days. How many months have 28 days?

Question: What has a head yet it never weeps, has a bed but never sleeps, can run but can not walks, and has a bank but not a cent to its name?

Question: What do thief's get for stealing calendars?

Question: Who was buried in Grant's Tomb?