How do I find the maximum value of $e^{-x^2+x}\cos(x^3+4)\cdot(x^4)$?

Question

I've put it through symbolab to derivate and obtained: $$ \frac{d}{dx}=e^{-x^2+x}(-2x+1)\cos(x^3+4)x^4+[-3x^6\sin(x^3+4)+4x^3\cos(x^3+4)]e^{-x^2+x}=0 $$ and then simplified to: $$ \frac{-2x^2+x+4}{3^3}=\tan(x^3+4) $$ Where can I go from here, if at all? (I apologize for any mistakes in my englsih)