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

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

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

The 138° angle is an exterior angle, so its adjacent interior angle is $180^\circ - 138^\circ = 42^\circ$.

Use triangle angle sum ($180^\circ$). Subtract the two known interior angles.
$m\angle1 = 180^\circ - 99^\circ - 42^\circ$

$41^\circ$