During the Christmas season a promotional company purchases cheap red felt stockings, glues fake white fur and sequins onto them and packages them for distribution.
The total cost of producing q cases of stockings is given by
c = 3q^2 + 50q − 18qlnq + 120
Find the number of cases that should be processed in order to minimize the average cost per case. Determine ( to two decimal places ) this minimum average cost.