Task: Question Answering
Input (English): Problem: in a school with 620 students , the average age of the boys is 12 years and that of the girls is 11 years . if the average age of the school is 11 years 9 months , then the number of girls in the school is 
Options: a ) 150 , b ) 200 , c ) 155 , d ) 350 , e ) none
Output (English): c