The degree of an arc is equal to the measure of the central angle that creates it, then to find the angle of arc MAC, we need to find the measure of the central angle MEC.
The segment NM is a diameter of the circle, then it is a straight line, the angle MEN measures 180° and it is equal to:
The central angle MEC, creates the arc MAC, then the measure of the angle of arc MAC is 115°.