Angle measure labeled a
The arc mesure labeled c

a = 24°

Step-by-step explanation:

Draw a radius from to the end of the chord.

The angle in the small sector is equal to the arc angle of 48°

The exterior angle is the supplement 180 - 48 = 132°

The isosceles triangle has two angles a of (180 - 132)/2 = 24°

This can be generalized to the angle between the chords is half of the arc angle when one chord is a diameter and the chords share a common endpoint.