There are 36 possible combinations for 2 dices because there are 6 numbers per di
6 has 5 combinations because you must use 2 dices
1+5
2+4
3+3
4+3
5+1
So Alex has

or

chance of getting exactly 6
While 9 has 4 combinations
3+6
4+5
5+4
6+3
So you have

or

chance of getting exactly 9
So Alex has a better chance