Arc Length and Chord Length

Find the magnitude, in degrees and minutes, of the angle subtended at the centre of a circle of radius length 30 cm, by a chord of length 50 cm.

I know that the formula to work out the chord length is $\displaystyle 2r\sin\frac{\theta}{2} $

$\displaystyle \theta $ is radians

So I get

$\displaystyle \frac{5}{6} =\sin\frac{\theta}{2} $

What do I do now?

I'm new to all this radian stuff (I'm completely clueless). I only know how to convert degrees to radians and vice versa