For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 100 units raises the average to 55 units per day, what is the value of n?  Choose the most appropriate option.
A) 6	B) 7	C) 8	D) 9	E) 10

Rationale: "the daily production was raised by 5 units for n days , which has a weighting of 5 n . 5 n = 100 - 55 = 45 n = 9 the answer is d ."
Answer: D