In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: to fill a tank , 25 buckets of water is required . how many buckets of water will be required to fill the same tank if the capacity of the bucket is reduced to 3 / 10 of its present ? 
Options: a ) 61.5 , b ) 60.5 , c ) 63.5 , d ) 83.333 , e ) 64.5
Example Output: d

Example Input: Problem: a car takes 6 hours to cover a distance of 504 km . how much should the speed in kmph be maintained to cover the same direction in 3 / 2 th of the previous time ? 
Options: a ) 48 kmph , b ) 50 kmph , c ) 52 kmph , d ) 56 kmph , e ) 60 kmph
Example Output: d

Example Input: Problem: a copy machine , working at a constant rate , makes 35 copies per minute . a second copy machine , working at a constant rate , makes 75 copies per minute . working together at their respective rates , how many copies do the two machines make in half an hour ? 
Options: a ) 90 , b ) 2,700 , c ) 3,300 , d ) 5,400 , e ) 324,000
Example Output:
c