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 river boat leaves silver town and travels upstream to gold town at an average speed of 3 kilometers per hour . it returns by the same route at an average speed of 7 kilometers per hour . what is the average speed for the round - trip in kilometers per hour ? 
Options: a ) 4.2 , b ) 7.1 , c ) 7.2 , d ) 7.5 , e ) 8.0

Output: a


Input: Consider Input: Problem: if the wheel is 21 cm then the number of revolutions to cover a distance of 1056 cm is ? 
Options: a ) 8 , b ) 27 , c ) 10 , d ) 7 , e ) 19

Output: a


Input: Consider Input: Problem: a , b , c can do a piece of work in 11 days , 20 days and 55 days respectively , working alone . how soon can the work be done if a is assisted by b and c on alternate days ? 
Options: a ) 2 , b ) 4 , c ) 8 , d ) 10 , e ) 12


Output: c