If you mix $\pu{20 ml}$ of $\pu{3 M}$ sugar solution with $\pu{30 ml}$ of a $\pu{5 M}$ sugar solution, what solution do you end up with?

What I did,

\begin{align}
\text{volume} &= \frac{\text{amount of substance}}{\text{concentration}}\\
\dfrac{3}{0.02} &= 150\\
\dfrac{5}{0.03} &= 166.\overline{6}\\
150+166.\overline{6} &= 316.\overline{6}
\end{align}

This is the wrong answer.
Any formulas which could help would be appreciated.