Answer:
D
Explanation:
B could fool you into picking it. The way B is done would give you an estimate for not 3 but 9 walls. So be wise. Don't choose B.
D is a much better choice. First of all, the question is an estimation question. The walls are approximately 10 * 14. Ivan might be safer in using 15 instead of 14, but the best answer is 3 * 140. or D