Whitney received $75,000 of taxable income in 2020. All of the income was salary from her employer. What is her income tax liability in each of the following alternative situations? Use Tax Rate Schedule for reference. (Do not round intermediate calculations.) a. She files under the single filing status. b. She files a joint tax return with her spouse. Together their taxable income is $75,000. c. She is married but files a separate tax return. Her taxable income is 75,000. d. She files as a head of household