Suppose that the labor cost for a building is approximated by C(x,y) = 2x + 5y - 80x - 420y + 26,000, 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. O A. x= 210, y = 126 O B. x= 20, y= 42 O C. x= 42, y = 210 O.D. x= 40, y= 84