CAT 2016 Quantitative Ability

Let the original volume of the raindrop be $\prime \mathit{x}\prime$ ml.
Therefore, initial volume of water in the raindrop will be $0.75\mathit{x}$ ml.
Remaining volume of water after evaporation= $\left(0.75\mathit{x}-2\right)$ ml
Remaining volume of water is 70% of $\left(\mathit{x}-2\right)$ ml.
$0.75\mathit{x}-2=\left(\mathit{x}-2\right)\times 0.7$
$\Rightarrow \mathit{x}=12$ .