Week $5$ Written Assignment: Suppose the total cost C$($x$)($in dollars$)$ to manufacture a quantity x of weed killer $($in hundreds of liters$)$ is given by C$($x$)=-2$x$^(2)+8$x$+50$ where x$>0.$ Where is C$($x$)$ decreasing? Where is C$($x$)$ increasing? Show step by step solutions and interpret your results in words. Find the second derivative of the following function f$($x$)=$x$^(4)-2$x$^(3)+3$x$^(2)-15.$ Show all detailed steps of solution $($show all work$).$