Answer:
(1). The reason is Because Apple's Profit are maximized where the publishers profits are maximized.
(2). Check last paragraph.
Step-by-step explanation:
To be sincere really, Apple is not really helping the publishers. From the question above we can see that the company that is Apple do collects a 30% commission on the price of a book from each of the United States of America publishers. Therefore, IF the price is INCREASED, Apple will make more commission/profit.
The answer to the second part of the question is that; With Apple's commission, the price that a book cartel will want to set will be be done make making sure that OUTPUT are RESTRICTED to where Marginal revenue is zero that is to say profit plus the 30% commission.