Given :
The figure of the circle N
As shown:
the measure of the angle JNK = the measure of the angle MNL = 21
Both of the angles are central angles
The measure of the arc = the measure of the central angle opposite to that arc.
Angle JNM and angle JNK are supplementary angles.
So, the measure of the arc JK = 21
The measure of the arc JNM = 180 - 21 = 159
The measure of the arc KL = the measure of the arc JNM = 159
Beacuse of the vertex angles are congruent.