Calculate the angle

Math with Alex | Geometry with Alex | Geometry Olympiad Problems | solving geometry problems | advanced geometry problems | Premath | Math Queen | Math Booster | geometry tutor | math olympiad preparation | math contest preparation | triangle angles | isosceles triangle | interior angle sum | geometry problem | angle calculation | triangle properties | Euclidean geometry | math problem solving | step by step solution | school mathematics | exam preparation | angle rules | geometry tutorial | algebra geometry | logical reasoning | proof based geometry | triangle theorems | basic geometry | math education | angle sum theorem | SAT Problems