The average cost per item, C, in dollars, of manufacturing a quantity q of cell phones is given by
C= (a/q) + b
where a and b are positive constants
a.Find the rate of change of C as q increases. What are its units?
b. Currently, 5000 phones are being made and production is increasing at a rate of 100 cell phones per week. How fast is the average cost changing if a = 200000? Is the average cost increasing or decreasing?