An illustration shows two parallel slanting lines m and l intersecting a vertical line k. The angles formed at the intersection of lines l and k are 1, 2, 4, and 3. The angles 1 and 4 are opposite to each other while angles 2 and 3 are opposite to each other. The angles formed at the intersection of lines m and k are 5, 6, 8, and 7. The angles 5 and 8 are opposite to each other while angles 6 and 7 are opposite to each other.
If m∠6=140°, what is m∠7?
A. 40°
B. 140°
C. 50°
D. 180°
Since ∠6 and ∠7 are opposite angles, they are congruent. Therefore, m∠7 = m∠6 = 140°.
Answer: \boxed{\text{(B) } 140\degree}.