Answer:
x = 17
Explanation:
The sum of the angles in a triangle = 180°, thus
∠ECD = 180 - (100 + x) = 180 - 100 - x = 80 - x
∠ACB = 180 - (49 + 4x) = 180 - 49 - 4x = 131 - 4x
∠ECD = ∠ACB ( vertical angles are congruent ), that ia
80 - x = 131 - 4x ( add 4x to both sides )
80 + 3x = 131 ( subtract 80 from both sides )
3x = 51 ( divide both sides by 3 )
x = 17