$N=\frac{3mx}{5P}\text{ and }\frac{3mx}{5P}=\frac{9x}{10P}$

$\left\{\begin{matrix}x=\frac{10NP}{9}\text{, }&P\neq 0\text{ and }m=\frac{3}{2}\\x=0\text{, }&P\neq 0\text{ and }N=0\end{matrix}\right.$

$\left\{\begin{matrix}m=\frac{3}{2}\text{, }&N=\frac{9x}{10P}\text{ and }x\neq 0\text{ and }P\neq 0\\m\in \mathrm{R}\text{, }&N=0\text{ and }x=0\text{ and }P\neq 0\end{matrix}\right.$