This is pretty easy to calculate using a little trigonometry. All you have to do is work out four points, the end points of the arcs. You already know where the arc centers are, and you have the radius and angle, so this is pretty easy.
Read up on Sine, Cosine and Tangent here.
Sine, Cosine, Tangent
Also read about the Pythagorean theorum here.
Pythagorean theorem - Wikipedia, the free encyclopedia
Hope this helps.