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'.

Ex Input:
Problem: pipes a and b can fill a tank in 3 and 4 hours . pipe c can empty it in 4 hours . if all pipes are opened together , then the tank will be filled in ?
Options: a ) 3 hr , b ) 1 / 2 hr , c ) 1 hr , d ) 9 / 7 hr , e ) 5 / 3 hr

Ex Output:
a

Ex Input:
Problem: maxwell leaves his home and walks toward brad ' s house at the same time that brad leaves his home and runs toward maxwell ' s house . if the distance between their homes is 72 kilometers , maxwell ' s walking speed is 6 km / h , and brad ' s running speed is 12 km / h . what is the distance traveled by maxwell when they meet in the middle ?
Options: a ) 14 , b ) 24 , c ) 16 , d ) 18 , e ) 20

Ex Output:
b

Ex Input:
Problem: a train 180 m long running at 75 kmph crosses a platform in 40 sec . what is the length of the platform ?
Options: a ) 687 , b ) 638 , c ) 683 , d ) 726 , e ) 267

Ex Output:
c