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

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°