13 Helen sold her investment property on August 1, 2018, at a gain of $100,000. Helen expects to owe $20,000 in additional income taxes on this sale. She plans on making estimated payments to cover the expected tax liability. Helen's first estimated tax payment would be due on which date? a) April 15, 2018 b) September 15, 2018 c) June 15, 2018 d) January 15, 2019