Response to the following problem:
On June 15, 2014, Sheridan filed his 2013 income tax return reflecting a tax of $10,500. On October 5, 2015, he filed an amended 2013 return showing an additional $6,400 of tax, which he paid with the amended return. On August 22, 2017, he filed a claim for a refund of $7,000.
How much Federal income tax can Sheridan recover on the amended return?