I've searched and searched for this type of question but I can't find an example.

Can somebody please show me how to do this type of question:

Let $\displaystyle f(x,y)=x^2+3xy+xy^3$ and let $\displaystyle {\bf v}=(1,2)$

Calculate $\displaystyle \frac{\partial^2f}{\partial {\bf v}^2}$

My exams start this week and I'm out of time. If somebody could help me with this that would be great.