A particle is to move in an xy plane, clockwise around the origin as seen from the

Question:

A particle is to move in an xy plane, clockwise around the origin as seen from the positive side of the z axis. In unit-vector notation, what torque acts on the particle if the magnitude of its angular momentum about the origin is
(a) 4.0 kg · m2/s,
(b) 4.0t2 kg · m2/s,
(c) 4.0 √t kg · m2/s, and
(d) 4.0/t2 kg · m2/s?