Obviously there are multiple solutions that support the tableau, I think, I found another one, using different bases of numbersystems
1 4 = 5 correct in a numbersystem based on 6
2 5 = 7 = 12 in a numbersystem based on 5
3 6 = 9 = 21 in a numbersystem based on 4
8 11 = 19 = 201 in a numbersystem based on 3
So if you consider the LEFT side of the equation as standard DECIMAL numbers and the RIGHT side as the expression in different number systems, starting with base six and then going down 1 per row "201" base 3 would qualify