Solve the Problem $C(x, y)=4 x^{2}+3 y^{2}-280 x-240 y+22,000$ , Where $x$

Multiple Choice

Solve the problem.
-Suppose that the labor cost for a building is approximated by $C(x, y) =4 x^{2}+3 y^{2}-280 x-240 y+22,000$ , where $x$ is the number of days of skilled labor and $y$ is the number of days of semiskilled labor required. Find the $x$ and $y$ that minimize cost $C$ .

A) $x=35, y=40$
B) $x=40, y=60$
C) $x=70, y=80$
D) $x=60, y=120$