Explanation:
remember some of the angle theorems inside a circle.
first of all, arc angles are the angles of the corresponding circle segments at the center of the circle (the angle between the lines from the points on the arc to the center).
and, of course, all the arc angles together around a circle are therefore 360°.
so,
(8x + 20) + 104 + arc angle KJP = 360
and then :
the opposite angle is half of the arc angle for the same points on the circle arc.
angle L = 5x + 1 is the opposite angle of K and P, and that is therefore half of the arc angle KJP.
5x + 1 = (arc angle KJP)/2
arc angle KJP = 2×(5x + 1)
and by using this in the first equation we get
(8x + 20) + 104 + 2×(5x + 1) = 360
8x + 124 + 10x + 2 = 360
18x + 126 = 360
18x = 234
x = 234/18 = 13