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 and b together can do a piece of work in 6 days and a alone can do it in 13 days . in how many days can b alone can do it ? 
Options: a ) 12 days , b ) 15 days , c ) 78 / 7 days , d ) 21 days , e ) 22 / 7 days

Output: c


Input: Consider Input: Problem: a can do a piece of work in 10 days . he works at it for 4 days and then b finishes it in 9 days . in how many days can a and b together finish the work ? 
Options: a ) 6 , b ) 7 , c ) 5 , d ) 4 , e ) 1

Output: a


Input: Consider Input: Problem: a boat moves upstream at the rate of 1 km in 20 minutes and down stream 1 km in 9 minutes . then the speed of the current is : 
Options: a ) 1 kmph , b ) 2 kmph , c ) 3 kmph , d ) 2.5 kmph , e ) 1.85 kmph


Output: e