Answer:
D.130°
Step-by-step explanation:
An arc measure ia an angle an arc makes with the circle's centre and is proportional to the angle it subtends to the circumference, arc length.
-Given that AC and BC are diameters, then [tex]\angle AOB =\angle DOC[/tex] since they are alternate angles.
[tex]\angle AOB =\angle dOC=180\textdegree\\\\3x-70=x+10\\\\x=40\textdegree[/tex]
#Since angles on one side of a diameter sum up to 180°, mBC is calculated as:
[tex](3x-70)+m\angle BC=180\\\\M\angle BC=180+70-3\times 40\\\\=130\textdegree[/tex]
Hence, mBC=130°
