Problem: bookman purchased 30 copies of a new book released recently , 10 of which are hardback and sold for $ 20 each , and rest are paperback and sold for $ 10 each . if 14 copies were sold and the total value of the remaining books was 240 , how many paperback copies were sold ? 
Options: a ) 8 , b ) 12 , c ) 6 , d ) 4 , e ) 5
b