Find Values Of $x$ And $y$ Such That Both $f_{x}(x, y)=0$ And $f_{y}(x, y)=0$

Multiple Choice

Find values of $x$ and $y$ such that both $f_{x}(x, y) =0$ and $f_{y}(x, y) =0$ .
- $f(x, y) =4 x^{3}-2 x y+8 y$

A) $x=4, y=96$
B) $x=4, y=48$
C) $x=2, y=48$
D) $x=2, y=96$