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 $f_{y}(x, y) =0$ .
- $f(x, y) =x^{2}+y^{2}+6 x-7 y$

A) $x=\frac{3}{2}, y=-7$
B) $x=3, y=-\frac{7}{2}$
C) $x=-3, y=\frac{7}{2}$
D) $x=-\frac{3}{2}, y=7$