Make yourself a table of sums for a pair of dice and think about how many ways each can happen (also think of the die as two different colors)
so: sum how many ways
2 1 (only 1+1)
3 2 (1+2 or 2+1)
4 3 (1+3, 3+1, 2+2)
5 4 (1+4, 4+1, 2+3, 3+2)
notice the pattern forming in each column
so: 6 5
7 6 it now goes back down
8 5
9 4
10 3
11 2
12 1
Now total completely how many ways to get all sums (add number of ways column) = 36
for your event (sum of at least 9) that means the sum can be 9, 10, 11, or 12. Add up the number of way for each sum 4 + 3 + 2 + 1 = 10
probability is success/total
P(at least 9) = 10/36 which reduces to 5/18