Find an approximated value for using a Taylors polynomial of third degree and estimate the error.

I thought of solving it by using

centered at

So

Then I evaluated it at x=9.03, so I get:

I don't know if this is right, I've tried with the calculator and it gives 3.00500.... Now, how do I estimate the error? just by resting to the value the calculator gives the one I get?