A girl standing on road holds her umbrella at 45 ° with the...

$\overset{\to}{v}rg = \overset{\to}{v}r - \overset{\to}{v}g$

From the above diagram, velocity of the raindrop wrt ground will be,

$\left|\overset{\to}{v}r\right| = \sqrt{{\left(15\sqrt{2}\right)}^{2} + {\left(15\sqrt{2}\right)}^{2}} = 30km{h}^{- 1}$

And velocity of the raindrop wrt the moving girl will be,

\left|\overset{\to}{v}rg\right| = 15\sqrt{2} = \dfrac{30}{\sqrt{2}}km{h}^{- 1}