Force F = (6.0 N) i hat + (-9.0 N) k hat acts on a pebble with position vector r = (0.90 m) j hat + (-0.6 m) k hat, relative to the origin.
(a) What is the resulting torque acting on the pebble about the origin?
(b) What is the resulting torque acting on the pebble about a point with coordinates (-2.0 m, 6.0 m, 3.0 m)?