15. Find x.

Triangle OKN is a right-angled triangle with angle OKN = 90 degrees. The arc MN is 120 degrees, so the central angle MON = 120 degrees. Since OK is perpendicular to MN, OK bisects angle MON. Thus, angle MOK = angle NOK = 120 / 2 = 60 degrees. In triangle OKN, ON is the hypotenuse (radius). We have OK = ON * cos(60) and KN = ON * sin(60). We are given OM = 2.8, which is the radius. So ON = 2.8. Then x = KN = 2.8 * sin(60) = 2.8 * (sqrt(3)/2) = 1.4 * sqrt(3).