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: twelve machines , each working at the same constant rate , together can complete a certain job in 6 days . how many additional machines , each working at the same constant rate , will be needed to complete the job in 3 days ?
Options: a ) 14 , b ) 12 , c ) 15 , d ) 16 , e ) 18
Example Output: b

Example Input: Problem: a train 110 m long is running with a speed of 24 km / hr . in what time will it pass a man who is running at 6 km / hr in the direction opposite to that in which the train is going ?
Options: a ) 7 sec , b ) 6 sec , c ) 8 sec , d ) 14 sec , e ) 13.2 sec
Example Output: e

Example Input: Problem: on a trip covering 450 km , a bicyclist travels the first 300 km at 20 km per hour and the remainder of the distance at 15 km per hour . what is the average speed , in km per hour , for the entire trip ?
Options: a ) 16.5 , b ) 17.0 , c ) 17.5 , d ) 18.0 , e ) 18.5
Example Output:
d