What you really want to know is:
What is the net force ACTING ON the book ?
The answer is:
Before you ask how much net force there is, you should decide if there IS any net force.
-- If there's any net force acting on the object, then the object is accelerating.
-- If the object is not accelerating, then there is no net force acting on it.
-- The book is just laying there on the table. It is not accelerating. So there is definitely NO net force acting on it.
