Calvin miscalculated his income in 2013 and overpaid his state income tax by $10,000. In 2015, he amended his 2013 state income tax return and received a $10,000 refund and $900 interest. Calvin itemized his deductions in 2013, deducting $12,000 in state income tax and $30,000 total itemized deductions. ?Determine the effects of the above transactions to the taxpayer’s gross income in 2015. Explain.