Question 847202
P[multiple of 3 on the first die] =  1/3
ways to get a total of 8:

(2,6)
(3,5)
(4,4)
(5,3)
(6,2)

So 5/36 ways to sum to 8.

Notice that our roll of (3,5) is being counted in both cases so we must subtract it once. 

Putting it all together:
P[multiple of 3 on first, sum to 8] =  1/3 + 5/36 - 1/36 = 4/9