Question

1. find the missing angle measure.

Explanation:

Step1: Recall quadrilateral angle - sum property

The sum of the interior angles of a quadrilateral is $360^{\circ}$.

Step2: Assume the missing angle is $\angle D$

Let $\angle C = 60^{\circ}$, and assume the other two non - shown angles $\angle E$ and $\angle F$ are also unknown for now. But if we assume this is a parallelogram (since no other information is given and for simplicity, opposite angles in a parallelogram are equal), and if $\angle C$ and $\angle E$ are adjacent angles. In a parallelogram, adjacent angles are supplementary.

Step3: Calculate the missing angle

Since adjacent angles in a parallelogram add up to $180^{\circ}$, if $\angle C = 60^{\circ}$, then $\angle D=120^{\circ}$ (because $\angle C+\angle D = 180^{\circ}$).

Answer:

$120^{\circ}$