Assuming that you mean 3 as the decimal representation of the english word "three" ie: [tex]3_{d}[/tex] then you can solve this a couple of ways:
1. By rote memorizarion: 3x3=9
2. As repeated addition: 3+(3+(3)) = 9
3. Representing it as 3 'groups of' 3: (ooo)(ooo)(ooo)
4. As a square with sides of length three:
_ _ _
|_|_|_|
|_|_|_| = 9 squares
|_|_|_|
5. As "3 squared" [tex]3^{2} =9[/tex]
