The rate of flow (V) of a liquid (coefficient of viscosity is $\mathrm{\eta }$) flowing through a pipe of radius r , length L and pressure gradient p is given by Poiseuille's equation $\mathrm{V}=\frac{\mathrm{\pi }}{8}\frac{{\mathrm{r}}^{\mathrm{x}}}{{\mathrm{\eta }}^{\mathrm{z}}\mathrm{L}}{\mathrm{p}}^{\mathrm{y}}$. Then calculate the value of x.