The Inn occasionally hires Maria Sostenuto, a local pianist, to entertain the guests during the evening while they chat by the fireplace in the Grand Room. Maria charges $$300$ per apprearance plus $$30$ per hour.

$1.$ If Maria plays for three hours, what would be:

the total cost to the Inn?

the average cost per hour?

$2.$ If the Inn manager wants Maria to stay for a fourth hour, what would be:

the cost of the fourth hour $($the marginal cost$)?$

the total cost to the Inn?

the average cost per hour?

$3.$ Explain why the average cost is an unimportant calculation in this situation.