Task: Question Answering
Input (English): Problem: 20 one identical machines , running continuously at the same constant rate , take 9 days to complete a shipment . how many additional machines , each running at the same constant rate , would be needed to reduce the time required to complete a shipment by two days ? 
Options: a ) 2 , b ) 3 , c ) 4 , d ) 6 , e ) 9
Output (English): d