Correct Answer: 3
Explanation:
Given expression = 6 - [9 - {18 - (15 -12 - 9)}] = 6 - [9 - {18 - (15 - 12 + 9)}] = 6 - [9 - {18 - 12}] = 6 - [9 - 6] = 6 - 3 = 3
