Matrices & Systems · Hard problem

A logistics company's total shipping cost model is $\mathbf p^{T}(RS)\mathbf q$, where $\mathbf p = \begin{pmatrix}3\\1\end{pmatrix}$ is a demand profile, $\mathbf q = \begin{pmatrix}2\\5\end{pmatrix}$ is a region-weight vector, and $R = \begin{pmatrix}1 & 2\\0 & 3\end{pmatrix}$, $S = \begin{pmatrix}2 & 1\\1 & 4\end{pmatrix}$ are two processing-stage matrices. Find the total cost.