(a) $Fluid\ resistance\ is\ given\ by\ \ \ \ \ R = \frac{8ɳL}{{\pi r}^{4}}$
When two capillary tubes of same size are joined in parallel, then equivalent fluid resistance is
$R_{eq} = R_{1} + R_{2} = \frac{8ɳL}{{\pi R}^{4}} + \frac{8ɳ \times 2L}{\pi(2R)^{4}}$
Equivalent resistance becomes$\ \ \ \frac{9}{8}$ times so,$\ $
$rate\ of\ flow\ will\ be\frac{8}{9}X.$