What was the change in net book amount for software under development between 2018 and 2019?
{"Movements": {"Rights and licences": 0, "Internally generated software": 0, "Software under development": 0, "Total": 0}, "30 June 2019 -- Opening net book amount at 1 July 2018": {"Rights and licences": 13, "Internally generated software": 6385, "Software under development": 6509, "Total": 12907}, "30 June 2019 -- Additions  internally developed": {"Rights and licences": "-", "Internally generated software": "-", "Software under development": 11896, "Total": 11896}, "30 June 2019 -- Amortisation": {"Rights and licences": "-", "Internally generated software": -1116, "Software under development": "-", "Total": -1116}, "30 June 2019 -- Transfers between classes": {"Rights and licences": "-", "Internally generated software": 2121, "Software under development": -2121, "Total": "-"}, "30 June 2019 -- Disposals": {"Rights and licences": "-", "Internally generated software": -9, "Software under development": "-", "Total": -9}, "30 June 2019 -- Closing net book amount": {"Rights and licences": 13, "Internally generated software": 7381, "Software under development": 16284, "Total": 23678}}
software_closing = df["30 June 2019 -- Closing net book amount"]["Software under development"]
software_openning = df["30 June 2019 -- Opening net book amount at 1 July 2018"]["Software under development"]
answer = software_closing - software_openning