Rolling two dice can output any number between 2 and 12. Here are the probabilities (given by how many combinations would yield that sum):
You get 2 if you roll (1, 1)
You get 3 if you roll (1, 2), (2, 1)
You get 4 if you roll (1, 3), (2, 2), (3, 1)
You get 5 if you roll (1, 4), (2, 3), (3, 2), (4, 1)
You get 6 if you roll (1, 5), (2, 4), (3, 3), (4, 2), (5, 1)
You get 7 if you roll (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1)
You get 8 if you roll (2, 6), (3, 5), (4, 4), (5, 3), (6, 2)
You get 9 if you roll (3, 6), (4, 5), (5, 4), (6, 3)
You get 10 if you roll (4, 6), (5, 5), (6, 4)
You get 11 if you roll (5, 6), (6, 5)
You get 12 if you roll (6, 6) 
So, you get an even sum OR a 3 if you roll a total of 2, 3, 4, 6, 8, 10 or 12. The sum of their probabilities is

You get doubles and at least 8 if you get (4,4), (5,5) or (6,6). Each of these pairs happen with probability 1/36, for a total of
