9. The mines discussed in problem 8 have steadily gained sales in several countries and are shipping a larger volume of ore. Sea Lanes Shipping Services Ltd. has started using larger ships that require 1.25 days to load, but the average rate at which these ships arrive at the dock remains at 5.0 ships per week. The cost per idle day for these ships is $5,500 and the cost to operate each dock remains at $900 per day. Determine the number of docks the company should operate in order to minimize the sum of the ship delay and dock operating expenses. (Use Figure 15.5.)