Microeconomics - Determining how many items to sell

Hi,

I would really appreciate it if someone could help me with these questions:

An author earns royalties from his book that are specified as 10% of the book's selling price. The demand curve for this is straight and downward sloping.

1. What rule does the author want his publisher to follow in determining how many copies of book to sell?

2. The publisher want to determine how many copies of the book to sell so what rule does he follow?

3. Does the author or the publisher sell more books?