Task: Question Answering
Input (English): Problem: running at the same constant rate , 6 identical machines can produce a total of 270 pens per minute . at this rate , how many pens could 10 such machines produce in 4 minutes ? 
Options: a ) 1500 , b ) 1545.6 , c ) 1640.33 , d ) 1800 , e ) none of these
Output (English): d