Answer
x=3; y=3.
Work Step by Step
$f_{x}(x,y)=9y - 3x^{2} =0$
$f_{y}(x,y)=9x-3y^{2}=0$
Solving the first equation for yields $x^{2}=\frac{9y}{3} \rightarrow x=\sqrt 3y$
Substituting this into the second equation yields
$9(\sqrt 3y)-3y^{2}=0$
$y^{2}=3\sqrt 3y$
$y^{4}=27y$
$y=3$
$\rightarrow x=3$
