A progressive tax system has people pay no tax on incomes up to $10,000, 12% of income between $10,000 and $20,000, and 18% of all income above $20,000. a. Set up a piecewise-linear model for this progressive tax structure. Be sure to specify your variables. b. What does a person with an income subject to tax of $25,000 pay in taxes? c. How much tax does a person with income subject to tax of $30,000 pay?