Find the Indicated Maxima or Minima $f(x, y)=x^{2}+y^{2}-x y$ , Subject To

Multiple Choice

Find the indicated maxima or minima.
-Minimum of $f(x, y) =x^{2}+y^{2}-x y$ , subject to $x-y=10$

A) 75 when $x=5, y=-5$
B) 7 when $x=2, y=-1$
C) 3 when $x=1, y=2$
D) 25 when $x=5, y=5$