An undiscovered planet, many lightyears from Earth, has one moon in a periodic orbit. This moon takes 18.0days on average to complete one nearly circular revolution around the unnamed planet. The distance from the center of the moon to the surface of the planet is 2.34510^5km and the planet has a radius of3475km.

Determine the moon's centripetal acceleration _c.

a_c = ______________________________ m/s^2