+128399 We can first use the Law of Sines
sin 60 / 9.2 = sin B ' / 10
10 sin 60 / 9.2 = sin B ' take the arcsin to find B '
arcsin [ 10 sin 60 / 9.2 ] = B ' ≈ 70.27°
But B ' is obtuse so its true measure is 180 - 70.27 ≈ 109.73°
And since the triangle on the left is isosceles and the angle supplemental to 109.73°= 70.27°....then this will also be the measure of B
So
B = 70.27° and B ' = 109.73°
