Joe, Michael, Bill, and Edwin are making a beat by tapping their pens on the table.
Joe taps once every 2 seconds, Michael taps every 3 seconds, Edwin taps every 7 seconds, and
Bill taps every 6 seconds.
They do this beat for 5 minutes before their parents notice it and hushes them.
How many times could all 4 of them have tapped at the same time during this time?