Question

what is $m\angle 1$?
triangle with angles 101° and 31°, and angle 1 adjacent to the triangle
$m\angle 1 = \square^\circ$

Explanation:

Step1: Find the triangle's third angle

Let the unknown interior angle be $x$. The sum of angles in a triangle is $180^\circ$.
$$x = 180^\circ - 101^\circ - 31^\circ$$
$$x = 48^\circ$$

Step2: Calculate $\angle 1$ (supplementary to $x$)

$\angle 1$ and $x$ form a linear pair, so their sum is $180^\circ$.
$$m\angle 1 = 180^\circ - 48^\circ$$

Answer:

$132^\circ$