Answer
$-\dfrac{\pi}{6}$
Work Step by Step
We know that since $\sin{(-\frac{\pi}{6})}=-0.5$, then by the definition of the inverse function: $\sin^{-1}{(-0.5)}=-\frac{\pi}{6}$. (because it is in the right domain, in $[\frac{-\pi}{2},\frac{\pi}{2}]$)
