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: a hiker walked for 3 days . she walked 18 miles on the first day , walking 3 miles per hour . on the second day she walked for one less hour but she walked one mile per hour , faster than on the first day . on the third day 5 miles per hour for 6 hours . how many miles in total did she walk ? 
Options: a ) 68 , b ) 44 , c ) 58 , d ) 60 , e ) 62
Example Output: a

Example Input: Problem: 8 persons can build a wall 140 m long in 42 days . in how many days can 30 persons complete a similar wall 100 m long ? 
Options: a ) 12 , b ) 10 , c ) 8 , d ) 6 , e ) 5
Example Output: c

Example Input: Problem: two carpenters , working in the same pace , can build 2 desks in two hours and a half . how many desks can 4 carpenters build in 5 hours ? 
Options: a ) 2.4 . , b ) 3.6 . , c ) 4.2 . , d ) 8 . , e ) 6.4
Example Output:
d