Angles B, C, D, and E are inscribed angles and equal 1/2 the intercepted arc.
Angle C (87 degrees) is 1/2 the arc DEB
arc BED = 87 * 2 = 174 degrees
arc DE = 174 - 76 = 98 degrees
arc CB = 360 -60 -98 -76 = 126 degrees
Angle DEB = 1/2 * (60 + 126)
Angle DEB = 1/2 * 186
Angle DEB = 93 degrees
Source 1728.com/circangl.htm