Find the measure of each angle of a parallelogram, if one of its angles is 30°

 Let ABCD be a parallelogram. 
 ∴ ∠​A = ∠​C and ∠B = ∠D          (Opposite angles)
 Let ∠A be the smallest angle whose measure is xo.
 ∴​ ∠​B = (2x − 30)o
Now, ∠​A + ∠B = 180o                (Adjacent angles are supplementary) 
   ⇒ x + 2x − 30o = 180o
   ⇒ 3x = 210o
   ⇒ x = 70o
∴ ​∠​B = 2 ⨯ 70o − 30o = 110o
 Hence, ∠A = ∠C = 70o; ∠B = ∠D = 110o