On June 15, 2020, Sheridan filed his 2019 income tax return, paying a tax of $10,500. On October 5, 2021, he filed an amended 2019 return showing an additional $6,400 of tax, which he paid with the amended return. On August 22, 2023, he filed a claim for a refund of $7,000. Assuming that Sheridan is correct in claiming a refund, how much tax can he recover?