vector matrix

Every vector ${v}$ can be expressed uniquely in the form ${a+b}$, where ${a}$ is a scalar multiple of $\begin{pmatrix} 2 \\ -1 \end{pmatrix}$, and ${b}$ is a scalar multiple of $\begin{pmatrix} 3 \\ 1 \end{pmatrix}.$ Find the matrix ${P}$ such that ${Pv=a}$ for all vectors ${v}$.

Sorry if this is a dumb question, but does ${Pv}$ mean P * v, or P dot v?