∠1 and angle, 2∠2 are supplementary angles. If m, angle, 1, equals, left bracket, 2, x, minus, 21, right bracket, degreesm∠1=(2x−21)
∘
and m, angle, 2, equals, left bracket, 4, x, plus, 15, right bracket, degreesm∠2=(4x+15)
∘
, then find the measure of angle, 2∠2.