In a quadrilateral one angle is 120°, the remaining three angles are equal. Then the measure of each angle is

In a quadrilateral one angle = 120°
Let the other three angles be x°, x°, x°
The sum of angles in a quadrilateral = 360°
$\begin{array}{l}{120}^{\circ }+{\mathrm{x}}^{\circ }+{\mathrm{x}}^{\circ }+{\mathrm{x}}^{\circ }={360}^{\circ }\\ 3{\mathrm{x}}^{\circ }={360}^{\circ }-{120}^{\circ }\\ 3\mathrm{x}={240}^{\circ }\\ \mathrm{x}={80}^{\circ }\end{array}$