In a particle accelerator, the position vector of a particle is initially estimated as $\vec{r}=6.0 \hat{\mathrm{i}}-7.0 \hat{\mathrm{j}}+3.0 \hat{\mathrm{k}}$ and after $10 \mathrm{~s}$, it is estimated to be $\vec{r}=-3.0 \hat{\mathrm{i}}+9.0 \hat{\mathrm{j}}-3.0 \hat{\mathrm{k}}$, all in meters. In unit vector notation, what is the average velocity of the particle?