Calculating Torque for a Particle in an xy Plane

[pippi1500]

Homework Statement

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 at time t = 2.1 s if the magnitude of its angular momentum about the origin is 2.5t² kg·m2/s3

Homework Equations

torque = dL/dt

The Attempt at a Solution

I tried taking the derivative of 2.5*t² and then I inserted t.

2*2.5*2.1 = 10.5 but this is not the correct answer and I'm not sure why.

 

[rock.freak667]

Did you put in just the number alone or the number with the unit vector?