Answer:
C. x = 40
Step-by-step explanation:
1. Get the supplementary angle of ∠9: 180 - m∠9 = 180 - (4x-10)
2. The inside angles of that triangle add up to 180: 30 + 3x + 180 - (4x-10) = 180
3. Solve for x:
30 + 3x + 180 - (4x-10) = 180
30 + 3x + 180 - 4x + 10 = 180 Distribute negative to parenthesis
220 - x = 180 Combine like terms
-x = -40 Subtract 220 on both sides
x = 40 Divide both sides by -1
