It's the parallelogram. Therefore
ML = JK, JM = KL, m∠L = m∠J, m∠M = m∠K and m∠M + m∠L = 180°.
ML = 21 → JK = 21
JM = 29 → KL = 29
m∠L = 127° → m∠J = 127°
m∠M + m∠L = 180° → m∠M + 127° = 180° → m∠M = 53°
m∠M = 53° → m∠K = 53°
