6,9,7,5的24点答案：
1:6 + (9 × (7 - 5))
2:6 + 9 ×(7 - 5)
3:6 - (9 × (5 - 7))
4:6 - 9 ×(5 - 7)
5:6 + (7 - 5) × 9
6:6 + ((7 - 5) × 9)
7:6 - (5 - 7) × 9
8:6 - ((5 - 7) × 9)
9:(9 × (7 - 5)) + 6
10:9 × (7 - 5) + 6
11:(7 - 5) × 9 + 6
12:((7 - 5) × 9) + 6