Task: Question Answering
Input (English): Problem: elena purchased brand x pens for $ 4.00 apiece and brand y for $ 2.20 apiece . if elena purchased a total of 12 of these pens for $ 42.00 , how many brand x pens did she purchase ? 
Options: a ) 4 , b ) 5 , c ) 6 , d ) 7 , e ) 8
Output (English): c