Here are the ways to get a sum of 4 or smaller
1+1 = 2
1+2 = 3
1+3 = 4
2+1 = 3
2+2 = 4
3+1 = 4
There are 3 items in the first block, 2 in the next, and 1 in the last.
There are 3+2+1 = 6 ways to achieve a sum of 4 or smaller.
There are 6*6 = 36 ways to roll two dice.
That gives 36-6 = 30 ways to get a sum of 5 or more. You can use a dice chart to verify.
Divide the values:
30/36 = 5/6 is the probability of getting a sum of 5 or larger.