For the past n days, the average (arithmetic mean) daily production at a company was 30 units. If today's production of 90 units raises the average to 35 units per day, what is the value of n ?	Choose the correct option.
A) 30  B) 18  C) 10  D) 9  E) 3
(average production for n days) * n = (total production for n days) --&gt; 30n=(total production for n days);   (total production for n days) + 90 = (average production for n+1 days) * (n+1) --&gt; 30n + 90 = 35 * (n+1) --&gt; n=3.   Answer: 3.
<result>E</result>
For the past n days, the average (arithmetic mean) daily production at a company was 30 units. If today's production of 90 units raises the average to 35 units per day, what is the value of n ?