Find the first partial derivatives of
$\displaystyle f(x,y) = \frac{x - 3y}{x + 3y}$ at the point $(x,y) = (1, 4)$.

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

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