[shatner]

I agree, it's puzzling. The only formula I've gotten to work so far was
1) Round income down to nearest 10: 52.6 becomes 50
2) Sequentially multiply by negative modifiers first: ((50 * .95) * .96) = 45.6
3) Sequentially multiply by positive modifiers: ((45.6 * 1.06) * 1.18) = 57.03648
4) Round result down: 57

And that's just me throwing those numbers into the formula-blender and taking whatever output looks right. I'll need more data points to test this or any other formula before I can be confident we've reverse-engineered the solution.

Also, are you sure the base income for that province is population/100? I ask because if the base number weren't 52.6 than it'd explain the difficulty we're having.