Task: Question Answering
Input (English): Problem: at a meeting , 25 attendants used a pencil and 15 attendants used a pen . if exactly 20 attendants used only one of the two types of writing tools , how many attendants wrote with both types of writing tools ? 
Options: a ) 10 , b ) 6 , c ) 7 , d ) 4 , e ) 14
Output (English): a