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

Input: Consider Input: Problem: a can contains a mixture of liquids a and b is the ratio 7 : 5 . when 9 litres of mixture are drawn off and the can is filled with b , the ratio of a and b becomes 7 : 9 . how many liter e of liquid a was contained by the can initially ? 
Options: a ) 10 , b ) 20 , c ) 21 , d ) 25 , e ) 27

Output: c


Input: Consider Input: Problem: if x and y are sets of integers , x # y denotes the set of integers that belong to set x or set y , but not both . if x consists of 12 integers , y consists of 18 integers , and 6 of the integers are in both x and y , then x # y consists of how many integers ? 
Options: a ) 6 , b ) 16 , c ) 18 , d ) 30 , e ) 174

Output: c


Input: Consider Input: Problem: in a group of 150 readers who read science fiction or literacy works or both , 120 read science fiction and 90 read literacy works . how many read both science fiction and literacy works ? 
Options: a ) 70 , b ) 60 , c ) 90 , d ) 100 , e ) 110


Output: b