Answer: X = 21°
Explanation:
If the whole of a triangle is 180°, then if you subtract 100 from 180 it leaves you with 80. From there you create the equation: x-4+3x=80. From there you add 4 to both sides which equals: x+3x=84. Then you combine like terms and get: 4x=84. Finally you divide the equation by 4 and get: x = 21