Question

estimate the measure of this angle within 15°,

Explanation:

Step1: Recall angle types

A right - angle is $90^{\circ}$, a straight - angle is $180^{\circ}$.

Step2: Estimate the angle

The given angle is larger than a right - angle ($90^{\circ}$) but smaller than a straight - angle ($180^{\circ}$). By visual comparison (using mental benchmarks like $30^{\circ}$ increments), it is closer to $120^{\circ}$ than to $90^{\circ}$ or $150^{\circ}$.

Answer:

$120^{\circ}$