Answer:
![\angle B=150^(\circ)](https://img.qammunity.org/2023/formulas/mathematics/high-school/h6ymqge7sxgbj7f4877nftnhk2x2qda553.png)
Explanation:
The diagram is two parallel lines cut by a transversal therefore Angle A and Angle B are alternate interior angles, in this case meaning they are equivalent (because lines are parallel).
We can use this information to set up an equation:
![8x-10=3x+90](https://img.qammunity.org/2023/formulas/mathematics/high-school/rqiwog1ho5gfr1xxrxltisjd359are0azr.png)
Add 10 to both sides:
![8x=3x+100](https://img.qammunity.org/2023/formulas/mathematics/high-school/u1fwwh4l47mqipofv76363sefbhdvhuzlp.png)
Subtract 3x from both sides
![5x=100](https://img.qammunity.org/2023/formulas/mathematics/high-school/mowmko5599z37hg0x8khu5f5t8glqlts33.png)
Divide both sides by 5
![x=20](https://img.qammunity.org/2023/formulas/mathematics/high-school/otvww2o09b1qyegcnswgop1y82pbf6uftp.png)
Then, substitute 20 for x to solve for Angle B:
![\angle B=3(20)+90\\\angle B=60+90\\\angle B=150](https://img.qammunity.org/2023/formulas/mathematics/high-school/j67kbjk9sxnaoqxaqhj9jr6n53hdtecf0s.png)