Determining the radius of a circle from a given arc

The following arc is a part of a circle. You are to determine how large the circle is by finding its exact radius length.
Describe in full detail the steps you would take to determine the radius of the circle. Then carry out you plan and complete the drawing of the circle. Leave the construction lines visible (do not hide them) so that one can see and relate to your explanation. Save your Geogebra file and copy the image (completed circle) you created, and paste it to include it in your Google document for your journal entry.