Here's the solution,
the angles made by same arc on circle's circumference are equal.
So, Angle O = Angle P
( Angles made by arc NM )
=》

=》

=》

=》

now, value of angle at circumference :
=》

=》

=》

=》

and, we know that the angle made by an arc at center is double the angle made by same arc on its circumference,
so, measure of Arc NM
=》

=》
