Answer:
Gravitational potential energy
Step-by-step explanation:
The book is put 5 feet in the air, which means 5 feet above the ground. An object which is located to a certain height above the ground possesses a form of energy called gravitational potential energy, which is the energy due to the fact that the object has "potential" to transform this energy into other forms of energy (e.g. kinetic energy, if the book is released and it starts moving).
The value of the gravitational potential energy of the object is given by the formula:

where
m is the mass of the object
g is the gravitational acceleration (9.8 m/s^2)
h is the height of the book above the ground (in this case, 5 feet)
So, we see that the gravitational potential energy is proportional to both the mass and the height of the object.