Task: Question Answering
Input (English): Problem: for the past n days , the average ( arithmetic mean ) daily production at a company was 50 units . if today ' s production of 90 units raises the average to 54 units per day , what is the value of n ? 
Options: a ) 30 , b ) 18 , c ) 10 , d ) 9 , e ) 7
Output (English): d