The problem involves drawing a free-body diagram: A book lies on a flat table. It is given that the weight of the book is 20N. I assume that since the book is not moving, the Fn (normal force) should also be 20N. The next part of the problem states that a string tied to the middle of the book pulls the book upward with a force of 15N. The question asks for the reaction forces in this case. I am confused to what the reaction force to the tension force of 15N. Any ideas?