6. P acquired HHH stock at various times and at various prices over the past three years as shown below. P sold 100 shares of HHH stock for $20,000 in 2020, but he cannot identify the particular shares that were sold. How much gain must P report on the sale?

P bought 50 shares of HHH stock in 2014 for $3,000.

In 2016 P bought 100 shares of HHH stock for $5,000

In 2018 P bought 200 shares of HHH stock for $9,000

In 2019 P bought 100 shares of HHH stock for $4,500