120=1/6*n3+1/2*n2+1/3*n+0 how do you do this?

Well the answer is n=8

I got this from the graph

https://www.desmos.com/calculator/ncyzikps9l

I also got it from our web2.0calc    

$${\frac{{{\mathtt{n}}}^{{\mathtt{3}}}}{{\mathtt{6}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{{\mathtt{n}}}^{{\mathtt{2}}}}{{\mathtt{2}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{n}}}{{\mathtt{3}}}}{\mathtt{\,-\,}}{\mathtt{120}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{n}} = {\mathtt{\,-\,}}{\frac{\left({\sqrt{{\mathtt{239}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{11}}\right)}{{\mathtt{2}}}}\\ {\mathtt{n}} = {\frac{\left({\sqrt{{\mathtt{239}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,-\,}}{\mathtt{11}}\right)}{{\mathtt{2}}}}\\ {\mathtt{n}} = {\mathtt{8}}\\ \end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{n}} = {\mathtt{\,-\,}}\left({\frac{{\mathtt{11}}}{{\mathtt{2}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{7.729\: \!812\: \!416\: \!869\: \!953}}{i}\right)\\ {\mathtt{n}} = {\mathtt{\,-\,}}{\frac{{\mathtt{11}}}{{\mathtt{2}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{7.729\: \!812\: \!416\: \!869\: \!953}}{i}\\ {\mathtt{n}} = {\mathtt{8}}\\ \end{array} \right\}$$