When you are using the same 2 numbers on 2 grids, you will get a difference on 8 between the 2 totals. My logic for this is when you look at the grids using the same 2 numbers you would see that the difference between them is 2. Then, if you look at the amount of numbers in the box (6 and 10) they have a difference of 4. When you times the 4 by the 2 you get 8. that is how you get the solution.
If you use 3 as the difference between two numbers(e.g.3 and 6) you get two totals (78 and 66).
The difference between is 12 and my logic for this is:
when you get the difference between 3 and 6 you get 3 and when you find the difference between the amount of numbers there is (6 and 10) you get 4.
When you times the 3 by the 4 you get 12 and that is how you get the difference.