Question

Three angles of a quadrilateral are equal and the measure of fourth angle is 120° . find the measure of each of equal angles

Answer 1

let same angles b x 
other angle is 120
sum of angles in a quadrilateral is 360
x+x+X+120=360
3x+120=360
3x=360-120
x=240/3
x=80

Answer 2

∵ the three angles are equal 
∴we will take all the equal three sides=3a
 ⇒a+a+a+120°=360°
⇒3a=360°-120°
⇒3a=240°
⇒a=240°/3
⇒a=80°
∴all the equal angles are of 80°.
         i hope this will help u