Question

what is $m\angle 1$?
$m\angle 1 = \square^\circ$

Explanation:

Step1: Find the triangle's third angle

Let the unknown interior angle be $x$. The sum of angles in a triangle is $180^\circ$.
$$x = 180^\circ - 37^\circ - 91^\circ = 52^\circ$$

Step2: Find $\angle1$ (supplementary to $x$)

$\angle1$ and $x$ form a linear pair (sum to $180^\circ$).
$$m\angle1 = 180^\circ - 52^\circ = 128^\circ$$

Answer:

$128$