You should be able to note that this is a parabola which opens downward. Taking the derivative and setting it to -0- will yield the max of the equation, That is
[tex]y=-\frac{1}{3} x^{2} +2x-4[/tex] ⇒ [tex]\frac{dy}{dx} =-\frac{2}{3} x+2=0[/tex] ⇒ [tex]x=3[/tex]
