A tiny rock is orbiting another 9.0 kg rock in a circular trajectory with a radius of 42 cm in a region of space unaffected by the gravity of other celestial objects. Both of the rocks are roughly spherical. Determine the time in which the tiny rock completes one revolution around the other rock.

[The value of the gravitational constant G = 6.67 x 10^-11 Nm²/kg²]