Six lights begin to flash together at 12:00 noon and flash respectively at intervals of 4, 5, 6, 7, 8, and 9 seconds. Not including the flash at 12:00 noon, how many more times will all six lights flash together before 4:00 pm (i.e. four hours later)?
Choose the correct choice from the following choices.
A) 3
B) 5
C) 7
D) 9
E) 11
The least common multiple is 2*2*2*3*3*5*7= 
<gadget id="calculator">2*2*2*3*3*5*7</gadget>
<output>2_520</output>
2520.   14400 seconds / 2520= 5 + remainder.   The answer is 5.
<result>B</result>
Six lights begin to flash together at 12:00 noon and flash respectively at intervals of 4, 5, 6, 7, 8, and 9 seconds. Not including the flash at 12:00 noon, how many more times will all six lights flash together before 4:00 pm (i.e. four hours later)?