Kathy received a commission of $12,000 from her employer and she also earns semimonthly wages of $2,500. Which of the following federal withholding methods is incorrect?

• If taxes have already been withheld from Kathy's wages separately, the commission is added to the wages and federal taxes are withheld as if the total were a single payment. Subtract the tax already withheld and withhold the remaining tax from the supplemental wages.

• If taxes have not already been withheld from Kathy's regular wage, the commission is added to the wages and withheld as if the total were a single payment.

• If taxes have already been withheld from Kathy's wages separately, the commission is taxed at a flat rate of 22%.

• If taxes have already been withheld from Kathy's wages, the commission is taxed at a flat rate of 28%.