Vector algebra

Given two vectors, $\vec{V}$ and $\vec{W}$, with norms, v and w respectively. The angle between them is $\phi$
a) Find the norm of the vector $\vec{V}$-$\vec{W}$, i.e. $| \vec{V}-\vec{W}|$.
b) Find the angle $\psi$ between the vectors  $\vec{V}-\vec{W}$ and $\vec{V}$.
c) Calculate (a) and (b) for:
v=12 w=9
and
$\phi=0 , \frac{\pi}{6} , \frac{\pi}{2} , \pi$
d) Draw the vectors $\vec{V}$$\vec{W}$ and $\vec{V}-\vec{W}$ for  $\phi=\frac{\pi}{6}$ .