Answer
$m∠A=m\angle C =69^{\circ}$
Work Step by Step
we know sum of all three angles of triangle is $180^{\circ}$
$m∠A+m∠B+m∠C$=$180^{\circ}$
$m\angle A+42^{\circ}+m\angle C$ = $180^{\circ}$
$m∠A+m\angle C $= $180^{\circ}−42^{\circ}$
$m∠A+m\angle C $ = $138^{\circ}$
$m∠A=m\angle C= 138^{\circ}\div2 =69^{\circ}$
