However, it looks like you can also subtract the first from the second row
Except for the first three rows, you subtracted the second from the first (also, column, not row). You would have to reword it as "add the third column to the absolute difference between the first and second column".
Given any set of numbers, it's always possible to come up ...
4. Each dot on the dice which surrounds an inner dot counts as one. A 5 counts as 4 and a 3 counts as 2. For example, roll 3 has 3 5's and 1 3. This would be 3 * 4 + 1 * 2 = 14. Roll 6 then contains only 1 5, which makes 1 * 4 = 4.