Answer
$\frac{3\pi}{8}$
Work Step by Step
We know that $f^{-1}(f(x))=x$.
For inverse sine, the value of $x$ (angle measure) should be in the interval $\frac{-\pi}{2} \leq x\leq \frac{\pi}{2}$..
Hence,
$\sin^{-1}(\sin(\frac{3\pi}{8}))=\frac{3\pi}{8}$
