Let $M$ be a marketed asset that is also a pricing asset such that for every marketed payoff $x$ there holds $P_{x}=\mathrm{E}[M x]$. Show that it follows that

\[P_{x}=\frac{1}{R}\left\{\bar{x}-\frac{\operatorname{cov}(x, M)}{\sigma_{M}^{2}}\left[\bar{M}-P_{M} R\right]\right\}\]