If you have Mathematica of a sufficiently recent version installed then you can open an empty notebook and type
=Limit[(x^3 - 13 x^2 + 51 x - 63)/(x^3 - 4 x^2 - 3 x + 18), x -> 3]
and shift and enter to evaluate that. That leading "=" tells Mathematica to send the question off to WolframAlpha.com, get the result and then display it.
That comes back with -4/5
But there should be a little grey "+" in the upper right corner of that and if you click on that + it will give you more details. Part of those details is SOMETIMES a button button labelled "Step-by-step solution" and if you click on that then SOMETIMES you get a fairly detailed description of the steps taken to find that -4/5. In this case it isn't too bad. But for some problems there is no set of steps available, because the methods used just don't translate into anything you could use.
You can get similar information with a paid subscription to WolframAlpha.com but I myself have never seen a compelling enough clear enough description of all the additional features, other than getting to see some steps, I would get from subscribing and thus have not tried that. Your preference may differ.