Task: Question Answering
Input (English): Problem: a children ' s gift store sells gift certificates in denominations of $ 3 and $ 5 . the store sold ' m ' $ 3 certificates and ' n ' $ 5 certificates worth $ 93 on a saturday afternoon . if ' m ' and ' n ' are natural numbers , how many different values can ' m ' take ? 
Options: a ) 5 , b ) 7 , c ) 6 , d ) 31 , e ) 18
Output (English): c