Two tubes of radii r_1 and r_2, and lengths l_1 and l_2, respectively, are connected in series and a liquid flows through each of them in stream line…

Two tubes of radii $\displaystyle \mathrm{r}_1$ and $\displaystyle \mathrm{r}_2$, and lengths $\displaystyle \mathrm{l}_1$ and $\displaystyle \mathrm{l}_2$, respectively, are connected in series and a liquid flows through each of them in stream line conditions. $\displaystyle \mathrm{P}_1$ and $\displaystyle \mathrm{P}_2$ are pressure differences across the two tubes. If $\displaystyle P_2$ is $\displaystyle 4 P_1$ and $\displaystyle l_2$ is $\displaystyle \frac{l_1}{4}$, then the radius $\displaystyle r_2$ will be equal to :