Answer:
Explanation:
Given
- m∠ABC = x°
- m∠BCD = 25°
- m∠CDE = 55°
- m∠DEF = 3x°
Add two more parallel lines passing through points C and D.
Consider alternate interior angles formed by the four parallel lines.
The angles between the two middle lines are equal to:
- m∠BCD - m∠ABC = m∠CDE - m∠DEF
Substitute values and solve for x:
- 25 - x = 55 - 3x
- 3x - x = 55 - 25
- 2x = 30
- x = 15
m∠ABC = 15°