Question $5(1\mathrm{.}5$ points$)$ A company has a monopoly on the production and consumption of a product on the market with revenue based on the demand output $)>(0$ of product units $($units$)$ of $R=a{Q}^3+b{Q}^2+3240Q+100($unit: thousand VND$),$ where a and $b$ are two unknown constants that need to be determined

a$)$ Find the revenue if the marginal revenue at $Q=1$ is $3219$ and the marginal revenue at $Q=2$ is $3192.$

b$)$ Find the output level Q $)>(0$ that optimizes the company's revenue and determine that optimal revenue.