Change of Basis - Homework Question Please help me understand what is being asked, I feel I am missing something.

Compute the change of basis matrix for each of the bases, and use it to find the coordinate vector v with respect to B

a) B={(1,2), (1,-2)}, v=(-1,3), (n=2)

b) Same thing just in $R^3$. I Imagine if I understand for R$^2$ I can get this one by myself.

I see a Basis, but only one. All examples in my text and online say change from Basis B to Basis C, and give both bases. So I go and compute the transition matrix $P_B \rightarrow c $ By creating an augmented matrix $ \left[
      \begin{array}{c|c}
        C&amp;B\\
      \end{array}
    \right]$ And reduce it to get the inverse of B. Then I use $P_B \rightarrow c $ times [v]$_B$ to to change the coordiantes to [v]$_C$ But in this question, where C?? Or am I trying to answer a question that hasn't been asked?

Thanks.
They are probably assuming the other basis to be the canonical, $\{(1,0),(0,1)\}$.
They are probably assuming the other basis to be the canonical, $\{(1,0),(0,1)\}$.