The distribution of daily demand for rug-cleaning machines at a rental store is shown in the following table. Machines are rented by the day only. Profit on a rug cleaner is $10 per day. The store has four rug-cleaning machines.

a. Assuming that the stocking decision is optimal, what is the implied range of excess cost per machine per day?
b. Your answer from part a has been presented to the manager, who protests that the amount is too low. Does this suggest an increase or a decrease in the number of rug machines he stocks? Explain.