Tobias overpays his 2018 state tax by $500 and gets a refund of $510 ($510 plus $10 in interest) in 2019. How is this refund treated for income tax purposes?

a. $500 will be taxed at the state and federal levels

b. Only the $10 will be taxed at the state level, but $510 will be taxed at the federal level

c. $510 will be taxed at the state and federal levels.

d. $10 will be taxed at the state and federal levels, but only using the blind widower filing status rates