6

9(9-1)=72
8(8-1)=56
7(7-1)=42
6(6-1)=30

5(5-1)=20

4(4-1)=12

3(3-1)=6

If you can recite the 'multiplication table',it won’t be a hard question^^

You've disappointed me Nacir. I thought that you were the most intellegent person here. ;-)

yihsuan_liao's answer is right, I made a mistake in multiplication.

9=72
8=56
7=42
6=30
5=20
3=?

8*9=72

7*8=56

6*7=42

5*6=30

4*5=20 

3*4=12 4=12

2*3=6   3=6