3x and 6/x are positive integers

1. insufficient, since 6/3 = 2 and 6/1 = 6. Both 2 and 6 are even, so you would have at least two options for x.
2. 8/x is greater than 10 means x is smaller than 8/10 = 4/5. Since 3x is an integer, x is smth like a/3. For x to be smaller than 4/5, a has to be either 1 or 2. Both 8/(1/3) = 24 and 8/(2/3) = 12 are greater than 10. So 2 by itself is insufficient.

Now we need to check to see if both statements taken together are sufficient. Well, since from 2 we deducted that x can be either 1/3 or 2/3. We need to see which one fits "6/x is even".
6/1/3 = 18 - is even
6/2/3 = 1 - is odd.

So both statements taken together are sufficient.