set.seed$(123)$ a$)(15$ points$)$ Use the Newsvendor Model to set up and run a Monte Carlo simulation assuming that demand is Poisson with a mean of $40$ units per day. The cost per unit $($C$)$ is $$12,$ the selling price $($R$)$ is $$18,$ and the salvage value $($S$)$ is $$10.$ b$)(10$ points$)$ Suggest the optimal purchase quantity, visualize and explain the outcome.