A roofing crew can roof the house in 10 hours. Another crew can roof the house in 15 hours. How many hours will it take for both of them working together to roof the house?
Choose the correct choice from the following answers.
A) 6 B) 5 C) 8 D) 4 E) 9
Work hrs=6B/(6+B)= 150/25= 
<gadget id="calculator">150/25</gadget>
<output>6</output>
6   6nswer is 6
<result>A</result>
A roofing crew can roof the house in 10 hours. Another crew can roof the house in 15 hours. How many hours will it take for both of them working together to roof the house?