If $\displaystyle f(x,y,z) = 2xy+z^{2}$ and $\boldsymbol{u}$ is the unit vector in the direction of $\left<5,0,-3\right>$, then the directional derivative at the point $(1,-3,3)$ in the direction of $\boldsymbol{u}$ is

$f_{\boldsymbol{u}} \, (1,-3,3) = D_{\boldsymbol{u}} \, f(1,-3,3) =$