The angle measurements in the diagram are represented by the following expressions.
\qquad \blueD{\angle A=8x -10^\circ}∠A=8x−10
∘
start color #11accd, angle, A, equals, 8, x, minus, 10, degrees, end color #11accd \qquad \green{\angle B=3x + 90^\circ}∠B=3x+90
∘
start color #28ae7b, angle, B, equals, 3, x, plus, 90, degrees, end color #28ae7b

Solve for xxx and then find the measure of \greenD{\angle B}∠Bstart color #1fab54, angle, B, end color #1fab54: