Let R$($x$),$C$($x$),$ and P$($x$)$ be$,$ respectively, the revenue, cost, and profit, in dollars, from the production and sale of x items. If R$($x$)=4$x and C$($x$)=0\mathrm{.}002$x$^(2)+1\mathrm{.}8$x$+70,$ find each of the following. a