$$P = \frac { r } { t - 3 } ( t )$$
$\left\{\begin{matrix}r=\frac{P\left(t-3\right)}{t}\text{, }&t\neq 3\text{ and }t\neq 0\\r\in \mathrm{R}\text{, }&t=0\text{ and }P=0\end{matrix}\right.$
$P=\frac{rt}{t-3}$
$t\neq 3$
