Plot the function $f(x)=\frac{x^2-4x-7}{x^2-x-6}$ for $-6x6.$ Notice that the function has two vertical asymptotes. Plot the function by dividing the domain of $x$ into three parts: one from $-6$ to near the left asymptote, one between the two asymptotes, and one from near the right asymptote to $6.$ Set the range of the $y$ axis from $-20$ to $20.$