A person places a 2-lb book on a table that is tilted at 15° relative to the horizontal. S...

A person places a 2-lb book on a table that is tilted at 15° relative to the horizontal. She finds that if she exerts a very small force on the book as shown, the book remains in equilibrium, but if she removes the force, the book slides down the table. What force would she need to exert on the book (in the direction parallel to the table) to cause it to slide up the table?