how to calculate height between mid points on a chord and arc

Hi I am absolutely useless at math could someone please help me with this.

I am trying to build a shade house and need to get some steel bent. I need to provide the distance between the midpoint on the chord and the midpoint on the arc.

I have a chord length of 2.7mtrs and an arc length of 3.6mtrs. Goggling it gave me the formula c/s = sin(x)/x but I don't even know what that means. where c is the chord length and s is the arc length.

Sorry to sound dopey to all you maths gurus.