Answer
$0.2\pi\frac{\text{rad}}{\text{sec}}$.
Work Step by Step
We know that the ships can see a blinking light every $5$ seconds. There are $2$ lights, hence a complete rotation takes $10$ seconds.
Hence the rotation speed: $\frac{1\text{rev}}{10\text{sec}}=0.1\frac{\text{rev}}{\text{sec}}=0.1\frac{2\pi\text{rad}}{\text{sec}}=0.2\pi\frac{\text{rad}}{\text{sec}}$.
