Task: Question Answering
Input (English): Problem: for a certain exam , a score of 86 was 5 standard deviations above mean and a score of 67 was 2.5 standard deviations above mean . what was the mean score for the exam ? 
Options: a ) 50 , b ) 55 , c ) 48 , d ) 42 , e ) 49
Output (English): c