Task: Question Answering
Input (English): Problem: machine a takes 20 hours to complete a certain job and starts that job at 6 am . after four hour of working alone , machine a is joined by machine b and together they complete the job at 1 pm . how long would it have taken machine b to complete the job if it had worked alone for the entire job ? 
Options: a ) 9.99 , b ) 3,615 , c ) 3.62 , d ) 4.62 , e ) 6.14
Output (English): d