Mark's 2011 income tax return was filed on time on 4/15/2012. The tax due was $12,000. Mark paid $9,000 on 11/1/2013 and never paid the rest. On 3/5/2020 the taxpayer filed an amended return claiming that the tax should have been $8,000 rather than $12,000 (a $4,000 reduction). Is the claim for refund timely? How much of the claim for refund can be allowed