Carl can wash all the windows of his house in 6 hours. His wife Maggie can wash all the windows in 6 hours. How many hours will it take for both of them working together to wash all the windows?	Choose the correct answer:
A) 2 B) 2 1/4 C) 3 D) 4 1/2 E) 5
Work hrs=AB/(A+B)= 36/12= 
<gadget id="calculator">36/12</gadget>
<output>3</output>
3   Answer is 3
<result>C</result>
Carl can wash all the windows of his house in 6 hours. His wife Maggie can wash all the windows in 6 hours. How many hours will it take for both of them working together to wash all the windows?