+118723 The meaning of this question is not clear at all 
$$\\5.00*10^{-4}t^2+0.20t+40=30\\\\
\frac{5}{10^{4}}t^2+0.20t+40=30\\\\
t^2+0.04*10^{4}t+8*10^{4}=6*10^{4}\\\\
t^2+400t+80000=60000\\\\
t^2+400t+20000=0\\\\$$
$${{\mathtt{t}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{400}}{\mathtt{\,\times\,}}{\mathtt{t}}{\mathtt{\,\small\textbf+\,}}{\mathtt{20\,000}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = {\mathtt{\,-\,}}{\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
{\mathtt{t}} = {\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
\end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = -{\mathtt{341.421\: \!356\: \!237\: \!309\: \!504\: \!9}}\\
{\mathtt{t}} = -{\mathtt{58.578\: \!643\: \!762\: \!690\: \!495\: \!1}}\\
\end{array} \right\}$$
+118723 The meaning of this question is not clear at all
$$\\5.00*10^{-4}t^2+0.20t+40=30\\\\
\frac{5}{10^{4}}t^2+0.20t+40=30\\\\
t^2+0.04*10^{4}t+8*10^{4}=6*10^{4}\\\\
t^2+400t+80000=60000\\\\
t^2+400t+20000=0\\\\$$
$${{\mathtt{t}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{400}}{\mathtt{\,\times\,}}{\mathtt{t}}{\mathtt{\,\small\textbf+\,}}{\mathtt{20\,000}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = {\mathtt{\,-\,}}{\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
{\mathtt{t}} = {\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
\end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = -{\mathtt{341.421\: \!356\: \!237\: \!309\: \!504\: \!9}}\\
{\mathtt{t}} = -{\mathtt{58.578\: \!643\: \!762\: \!690\: \!495\: \!1}}\\
\end{array} \right\}$$
