4,6,3,9的24点答案：
1:4 × (3 - 6 + 9)
2:4 × ((3 - 6) + 9)
3:4 × (3 - (6 - 9))
4:4 × (3 + 9 - 6)
5:4 × ((3 + 9) - 6)
6:4 × (3 + (9 - 6))
7:4 × (9 - 6 + 3)
8:4 × ((9 - 6) + 3)
9:4 × (9 - (6 - 3))
10:4 × (9 + 3 - 6)
11:4 × ((9 + 3) - 6)
12:4 × (9 + (3 - 6))
13:(6 - 4) × (3 + 9)
14:(6 - 4) × (9 + 3)
15:(3 - 6 + 9) × 4
16:((3 - 6) + 9) × 4
17:(3 - (6 - 9)) × 4
18:(3 + 9 - 6) × 4
19:((3 + 9) - 6) × 4
20:(3 + (9 - 6)) × 4
21:(3 + 9) × (6 - 4)
22:(9 - 6 + 3) × 4
23:((9 - 6) + 3) × 4
24:(9 - (6 - 3)) × 4
25:(9 + 3 - 6) × 4
26:((9 + 3) - 6) × 4
27:(9 + (3 - 6)) × 4
28:(9 + 3) × (6 - 4)