Calculate ∂f ∂x , ∂f ∂y , ∂f ∂x (1, −1) , and ∂f ∂y (1, −1) when defined. (If an answer is undefined, enter UNDEFINED.) f(x, y) = 9,000 − 70x + 12y +7xy ∂f ∂x = Incorrect: Your answer is incorrect. ∂f ∂y = Incorrect: Your answer is incorrect. ∂f ∂x (1, −1) = Incorrect: Your answer is incorrect. ∂f ∂y (1, −1) = Incorrect: Your answer is incorrect.