$$q _ { n } = 5 \times n c = 5 \cdot 10 ^ { - 6 } c$$
$q_{n}=5cn\text{ and }5cn=\frac{c}{200000}$
$\left\{\begin{matrix}q_{n}=\frac{c}{200000}\text{, }&n=\frac{1}{1000000}\\q_{n}=0\text{, }&c=0\end{matrix}\right.$
$\left\{\begin{matrix}n=\frac{1}{1000000}\text{, }&q_{n}=\frac{c}{200000}\text{ and }c\neq 0\\n\in \mathrm{R}\text{, }&q_{n}=0\text{ and }c=0\end{matrix}\right.$
