[tex]\text{The two angles are supplementary, so their sum is~} 180^{\circ} \\\\m\angle A + m\angle B= 180^{\circ}\\\\\implies x+15+x-13 = 180\\\\\implies 2x +2 = 180\\\\\implies 2x = 180-2\\\\\implies 2x = 178\\\\\implies x = \dfrac{178}2\\\\\implies x = 89\\\\\text{Hence the measure of angle B is}~ \angle B = (89-13)^{\circ} = 76^{\circ}[/tex]
