Answer/Step-by-step explanation:
Okay, so this question really is a nightmare, because this image is just not possible. Like, literally, Z is or is not the center, you do or do not have enough info. Its a bad question. This is not your fault. If you don't care why its a bad question scroll down to "How could someone get 55°"
If Z is the center, BZ and CZ are radii and equal. Angle CBZ is 60° because
AngleABC + Angle CBZ = 180°
120° + CBZ = 180°
CBZ = 60°
That means AngleC is also 60°. And then, since 180° in a triangle, AngleCZB also must be 60°.
This makes AngleCZD 120°.
But if Z is the center and ArcCD is 115°, then AngleCZD should be 115°.
Contradiction! Angle CZD can't be both 120° and 115° something is wrong here. See image.
How could someone get 55°? Well, it is also not correct but... If ArcCD is 115° then AngleCZD is 115° (if Z is the center) So AngleCZB is 180°-115°, which is 65°.
AngleCBZ is 60°
60° + 65° + C = 180°
125 + C = 180
C = 55°