Answer
$m∠1$ = $90^{\circ}$
Work Step by Step
The measures of the three angles of a triangle equal $180^{\circ}$; therefore, if we have the measure of the other two angles, we can figure out the measure of $∠1$.
Let $x$ equal $m∠1$:
$33 + 57 + x = 180$
Add the constants on the left side together:
$90 + x = 180$
Subtract $90$ from each side to solve for $x$:
$x = 90$
$m∠1$ = $90^{\circ}$
