Find a possible formula for the function graphed below. Assume the function has only one $x$-intercept at the origin, and the point marked on the graph below is located at $\left( 2, \frac{-1}{3} \right)$. The asymptotes are $x = -4$ and $x = 1$. Give your formula as a reduced rational function.

$f(x) =$ help (formulas)