Task: Question Answering
Input (English): Problem: a is the average ( arithmetic mean ) of the first 7 positive multiples of 5 and b is the median of the first 3 positive multiples of positive integer n . if the value of a ^ 2 – b ^ 2 is zero , what is the value of n ? 
Options: a ) 5 , b ) 6 , c ) 10 , d ) 15 , e ) 20
Output (English): c