b
(b)Rate of flow of liquid \(V = \frac{P}{R}\)
where liquid resistance \(R = \frac{{8\eta l}}{{\pi {r^4}}}\)
For another tube liquid resistance
\(R' = \frac{{8\eta l}}{{\pi {{\left( {\frac{r}{2}} \right)}^4}}} = \frac{{8\eta l}}{{\pi {r^4}}}.16 = 16R\)
For the series combination
\({V_{New}} = \frac{P}{{R + R'}} = \frac{P}{{R + 16R}} = \frac{P}{{17R}}\) \( = \frac{V}{{17}}\).