Answer:
x = 11
Step-by-step explanation:
Theorem:
The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote interior angles.
Angle ABC is an exterior angle of the triangle.
Angles D and C are its remote interior angles.
m<ABC = m<D + m<C
12x - 2 = 57 + 7x - 4
Combine like terms on the right side.
12x - 2 = 7x + 53
Subtract 7x from both sides.
5x - 2 = 53
Add 2 to both sides.
5x = 55
Divide both sides by 5.
x = 11
Answer: x = 11
