Find the first partial derivatives of
$\displaystyle f(x,y) = \frac{x - 4y}{x + 4y}$ at the point $(x,y) = (4, 1)$.

$\displaystyle \frac{\partial f}{\partial x}(4, 1) =$

$\displaystyle \frac{\partial f}{\partial y}(4, 1) =$