Let x be the common angle of quadrilateral.
As per question,
\(\angle\)A = \(\angle\)B = \(\angle\)C + \(\angle\)D = 360°
x + x + x + 120° = 360°
3x = 360° - 120
3x = 240°
X = 240 / 3
= 80°
\(\angle\)A = \(\angle\)B = \(\angle\)C = 80°
So, Three Angles of quadrilateral whose measuring’s are equal is 80°.