Using the central angle theorem, we know that arc JK is equal to 21° (its central angle).
Additionally, angles JNM and JNK are supplementary angles

Angle JNM measures 159°.
We know that angles JNM and KNL are equal by vertical angles, which means the arc KL measures 159° because it's the subtended arc of that central angle (KNL).
Now, arc JKM would be the sum 180° + 21° = 201°.
Arc JKM measures 201°.
At last, arc MKL would be equal to the difference 360° - 21° = 339°.
Arc MKL measures 339°.