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'.

Input: Consider Input: Problem: a man can do a piece of work in 4 days , but with the help of his son he can do it in 3 days . in what time can the son do it alone ?
Options: a ) 12 days , b ) 6 days , c ) 5 days , d ) 4 days , e ) none of these

Output: a

Input: Consider Input: Problem: walking with 4 / 5 of my usual speed , i arrive at the bus stop 7 minutes later than normal . how many minutes does it take to walk to the bus stop at my usual speed ?
Options: a ) 12 , b ) 16 , c ) 20 , d ) 24 , e ) 28

Output: e

Input: Consider Input: Problem: the current in a river is 5 mph . a boat can travel 20 mph in still water . how far up the river can the boat travel if the round trip is to take 10 hours ?
Options: a ) 69 miles , b ) 88 miles , c ) 93,75 miles , d ) 100 miles , e ) 112 miles
Output: c