An astronaut stands at a position on the Moon such that Earth is directly over head and

Question:

An astronaut stands at a position on the Moon such that Earth is directly over head and releases a Moon rock that was in her hand.
(a) Which way will it fall?
(b) What is the gravitational force exerted by the Moon on a 1.0-kg rock resting on the Moon's surface?
(c) What is the gravitational force exerted by the Earth on the same 1.0-kg rock resting on the surface of the Moon?
(d) What is the net gravitational force on the rock?