What was the percentage change in AA rated security deposits between 2018 and 2019?
{"": {"30 June 2019": 0, "30 June 2018": 0}, "CASH AT BANK -- AA rated": {"30 June 2019": 398999, "30 June 2018": 417982}, "SECURITY DEPOSITS -- AA rated": {"30 June 2019": 8822, "30 June 2018": 4151}}
aa_2019 = df["SECURITY DEPOSITS -- AA rated"]["30 June 2019"]
aa_2018 = df["SECURITY DEPOSITS -- AA rated"]["30 June 2018"]
answer = (aa_2019 - aa_2018) / aa_2018 * 100.0