Answer:
The correct answer is:
Michigan.
Michigan is the state that had a flat state income tax in 2009.
Explanation:
A flat tax (short for flat-rate tax) is a tax system with a constant marginal rate, usually applied to individual or corporate income.
Flat tax benefits higher income brackets progressively due to decline in marginal value.
The state that had a flat state income tax in 2009 is:
Michigan.
Michigan is a flat-tax state that levies a state income tax of 4.25%