Step 1: Recall what what is the inscribed angle and arc measurement

          (or central  angle)

          NOTE:An inscribed angle is an angle whose vertex sits on the

                      circumference of a circle. The vertex is the common endpoint of

                      the two sides of the angle. 

                     central angle(arc measurement) is any angle whose vertex is

                    located at the center of a circle. 

Step 2: Identify the relation between these two angles.

            NOTE: The central angle is always twice the inscribed angle.

Step 3: Calculate the unknown angle by substituting the known value

              Inscribed angle =\frac{Central\ angle}{2}

              Inscribed angle =  \frac{13}{2}