In this task, you need to provide the correct option for a given problem from the provided options.

Example Input: Problem: pencils , pens and exercise books in a shop are in the ratio of 14 : 4 : 3 . if there are 140 pencils , the number of exercise books in the shop is : 
Options: a ) 30 , b ) 27 , c ) 35 , d ) 33 , e ) 37
Example Output: a

Example Input: Problem: find the ratio in which rice at rs . 7.20 a kg be mixed with rice at rs . 5.70 a kg to produce a mixture worth rs . 6.30 a kg ? 
Options: a ) 1 : 3 , b ) 2 : 3 , c ) 3 : 4 , d ) 4 : 5 , e ) none of these
Example Output: b

Example Input: Problem: in a class of 40 students , 10 did not opt for math . 15 did not opt for science and 2 did not opt for either . how many students of the class opted for both math and science ? 
Options: a ) 13 , b ) 15 , c ) 7 , d ) 17 , e ) 18
Example Output:
c