People are allowed to add an apple or take an apple from a large barrel. If people are only adding apples, the barrel can be filled in 5 hours. If people only take apples, the barrel can be emptied in 15 hours. If it is desired that the barrel should be filled, from empty, exactly 6 hours after people begin adding apples at 9:30am, then at what time should people begin taking apples?  Choose the most appropriate option:
A) 10:00am  B) 10:45am  C) 12:00pm  D) 12:30pm  E) 1:30pm
In 6 hours the amount of apples added equals to 6*1/5 = 6/5 of the barrel. So, 1/5 more than necessary, which should be compensated by people taking apples. To rid 1/5 of the apples people take, it will require   15/5= 
<gadget id="calculator">  15/5</gadget>
<output>3</output>
3 hours.   Therefore, people should begin taking apples at 9:30am + 6 hours - 3 hours= 12:30pm.   Answer: 12:30pm.
<result>D</result>
People are allowed to add an apple or take an apple from a large barrel. If people are only adding apples, the barrel can be filled in 5 hours. If people only take apples, the barrel can be emptied in 15 hours. If it is desired that the barrel should be filled, from empty, exactly 6 hours after people begin adding apples at 9:30am, then at what time should people begin taking apples?