Task: Question Answering
Input (English): Problem: matt gets a $ 1,600 commission on a big sale . this commission alone raises his average commission by $ 150 . if matt ' s new average commission is $ 400 , how many sales has matt made ? 
Options: a ) 9 , b ) 4 , c ) 5 , d ) 6 , e ) 7
Output (English): a