Your little brother holds a 2 kg water balloon over the railing of his 15 m high tree house. What is the gravitational potential energy of the water ballon?

A) 2kg x 9.8 m/s^2 x 15m

B) 2kg x 15m

C) 2kg + 9.8 m/s^2 + 15m

D) 2kg x 15m + 9.8 m/s^2