Answer
$x=2arcsin(\frac{y}{3})$
Work Step by Step
$y=3sin\frac{x}{2}$
Need to solve $x$ in order to find this divide the above equation by 3 both sides.
$sin\frac{x}{2}=\frac{y}{3}$
Apply definition of arcsine.
$\frac{x}{2}=arcsin(\frac{y}{3})$
$x=2arcsin(\frac{y}{3})$
