a) what is the value of the centripetal force acting on the moon?

b) the mass ofthe earth is 5.98x10^24 kg and the universal gravitational constant G is 6.67x10^-11 Nm^2kg^-2. What is the value of the gravitational force acting between the earth and moon?

c) why are the numerical answers to parts a) and b) the same?

Ok, I am fine with a), but b) is confusing me!! Can someone help me with the next few steps?