Use the appropriate Product Rule to evaluate the derivative, where

${\bf r}_{1}(t)=\left<-6 t,2,-t^{3}\right> , {\bf r}_{2}(t)=\left<6,e^{t},-2\right>$

$\frac{\,d}{\,dt}\left({\bf r}_1(t)\cdot {\bf r}_2(t)\right)=$