In the diagram, find the size of the angle marked a°

Correct Answer: Option B

Explanation

2 x s = 280°(Angle at centre = 2 x < at circum)
S = (frac{280^o}{2})
= 140°
< O = 360 – 280 = 80°
60 + 80 + 140 + a = 360°
(< in a quad); 280 + a = 360
a = 360 – 280
a = 80°