Task: Question Answering
Input (English): Problem: carl can wash all the windows of his house in 7 hours . his wife maggie can wash all the windows in 4 hours . how many hours will it take for both of them working together to wash all the windows ? 
Options: a ) 2 , b ) 2 1 / 4 , c ) 11 6 / 2 , d ) 4 1 / 2 , e ) 5
Output (English): c