If you want to find a value for X from which
$\displaystyle sin^-1(x) = 0.8$
I have graphed this, and is $\displaystyle X = .916$
Any help please
Your post makes no sense.
If you want to solve $\displaystyle \sin^{-1}x = 0.8 \Rightarrow x = \sin 0.8$ then use a calculator. I get x = 0.717 (correct to 3 decimal places) assuming you're measuring angle in radians.
Otherwise, please post the question exctaly as it appears in your book or wherever it is you got it from.