Average Velocity question?

Question

I've tried this equation and keep getting -12, but the oline homwork keeps returning it as incorrect..can anyone help?

The position of a particle moving along an x axis is given by x = 12.0t^2 - 4.00t^3, where x is in meters and t is in seconds

(i) Determine the average velocity of the particle between t = 0 and t = 3.00 s.

Answer 1

Yes me to

are you using v = 24t - 12t^2

but since it's distance is 0 at t0 and t3 it should be 0 avg v