Answer:
As shown in picture,
NP = NM = PQ
=> 2 triangles PNM and NPQ are isosceles
=> angle NMP = angle NPM => arc NP = arc NM
=> angle NQP = angle QNP => arc PQ = arc NP
=> arc NP = arc NM = arc PQ
Otherwise, we have:
arc NP + arc NM + arc PQ + arc MQ = 360 deg
(sum of all arcs on a circle)
=> 3 x arc NP + 120 = 360
=> arc NP = 240/3 = 80 deg
Hope this helps!
:)