New York state income tax is based on taxable income, which is part of a person's total income. The tax owed to the state is calculated using the taxable income (not total income). In 2005, for a single person with a taxable income between $20,000 and $100,000, the tax owed was $973 plus 6.85% of the taxable income over $20,000.

a. Consider a lawyer whose taxable income is 80% of her total income, $x, where x is between $85,000 and $120,000. Write a formula T(x), the taxable income.

b. Write a formula for L(x), the amount of tax owed by the lawyer in part (a).

c. Use L(x) to evaluate the tax liability for x=85,000 and compare your results to part (a).

I'm stuck on a, so I can't do b or c.