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} .