In Exercises $1-6,($ a express $d w / d t$ as a function of $t,$ both by using the Chain Rule and by expressing $w$ in terms of $t$ and differentiating directly with respect to $t .$ Then (b) evaluate $d w / d t$ at the given value of $t$.
$$w=\ln \left(x^{2}+y^{2}+z^{2}\right), \quad x=\cos t, \quad y=\sin t, \quad z=4 \sqrt{t};$ $t=3$$