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: it will take 16 days for mary to complete a certain task alone . she worked for 8 days before she was joined by her sister . both of them completed the remaining task in 2 and half days . if her sister had joined her when she started the task , how many days would it have taken ?
Options: a ) 6 , b ) 8 , c ) 2 , d ) 5 , e ) 4

Ex Output:
d

Ex Input:
Problem: a man ' s regular pay is $ 3 per hour up to 40 hours . overtime is twice the payment for regular time . if he was paid $ 180 , how many hours overtime did he work ?
Options: a ) 8 , b ) 5 , c ) 9 , d ) 6 , e ) 10

Ex Output:
e

Ex Input:
Problem: find avrg speed if a man travels at speed of 18 km / hr up and 24 km / hr dawn at an altitude of 300 m .
Options: a ) 25.8 , b ) 26.8 , c ) 27.8 , d ) 20.5 , e ) 21.8

Ex Output:
d