6 Brian, a self-employed individual, and his wife, Mary, who works for a CPA firm, have the following state income tax payments: $1,000 estimated state income tax paid in 2021 for tax year 2020 $4,500 estimated state income tax paid in 2021 for tax year 2021 $1,500 estimated state income tax paid in 2022 for tax year 2021 $2,000 withheld in 2021 from Mary's paychecks Refund of $600 received in 2021 for a 2020 state income tax overpayment. They did itemize deductions in 2020 and would have even without the state tax deduction. Balance due on their 2021 state income tax return of $1,400, paid April 1, 2022 a. What is the amount of Brian and Mary's state income tax itemized deduction for their 2021 Federal income tax return? b. Since Brian and Mary did itemize their deductions in 2020, how much of the $600 state income tax refund they received in 2021 would be taxable? c. If they had not itemized their deductions in 2020, how much of the $600 state income tax refund received in 2021 would be taxable