I'm stuck on this problem please help me

Question

find the range of this equation

y = (x^2 - 4)/(x^2 - x - 12)

I know that it is [1/3,-infintiy]U[?,infinity]
yes I'm having trouble with that ?
At first I was like ok there should be a horizontal asymptote at y=1 there is in calculus deffinition the image as x approaches infinity from both sides right? or is just infinity... but ya it appraoches one from both sides but it corsses one at x=-8 check the graph so how do I find how low it goes at this section also I can't use a calculator well I can but am suppose to show all work with out using one i.e. have one to use not suppose to use it thanks

also unless I'm doing something wrong when x=100 y is not one you told me it did I must be doing something wrong