A room has both an entrance and an exit door. The room can fill up with people in 5 hours. The room can be empty of people in 15 hours. If it is desired that the room should be filled, from empty, exactly 6 hours after people begin entering the room at 9:30am, then at what time should people begin exiting the room?	Choose the correct answer:
A) 10:00am B) 10:45am C) 12:00pm D) 12:30pm E) 1:30pm
In 6 hours the entrance door is opened to fill the room equal to 6*1/5 = 6/5 of the room. So, 1/5 more than necessary, which should be compensated by people using the exit door. To empty out 1/5 of the people, the exit door needs 15/5= 
<gadget id="calculator">15/5</gadget>
<output>3</output>
3 hours.   Therefore, the exit door should be used at 9:30am + 6 hours - 3 hours= 12:30pm.   Answer: 12:30pm.
<result>D</result>
A room has both an entrance and an exit door. The room can fill up with people in 5 hours. The room can be empty of people in 15 hours. If it is desired that the room should be filled, from empty, exactly 6 hours after people begin entering the room at 9:30am, then at what time should people begin exiting the room?