You can plug this into a calculator: $$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}^{\!\!\mathtt{-1}}{\left({\frac{{\sqrt{{\mathtt{3}}}}}{{\mathtt{2}}}}\right)} = {\mathtt{60^{\circ}}}$$
Or, you can use the unit circle (a circle with a radius of 1 which is very useful for finding exact values of angles with 30, 45, and 60 degree reference angles).
This page explains it more if you're interested: http://www.mathsisfun.com/geometry/unit-circle.html