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

Input: Consider Input: Problem: in a river flowing at 2 km / hr , a boat travels 40 km upstream and then returns downstream to the starting point . if its speed in still water be 6 km / hr , find the total journey time . 
Options: a ) 10 hours , b ) 12 hours , c ) 14 hours , d ) 15 hours , e ) none of these

Output: d


Input: Consider Input: Problem: 54671 - 14456 - 35466 = ? 
Options: a ) 2449 , b ) 5449 , c ) 6749 , d ) 6449 , e ) 4749

Output: e


Input: Consider Input: Problem: find the average of first 15 natural numbers . 
Options: a ) 10 , b ) 120 , c ) 15 , d ) 8 , e ) 16


Output: d