What is the percentage change in the company's prepaid expenses between 2018 and 2019?
{"Prepaid expenses": {"September 2019": 1.8, "September 2018": 1.6}, "Prepaid inventory": {"September 2019": 5.3, "September 2018": 3.3}, "": {"September 2019": 7.1, "September 2018": 4.9}}
prepaid_expenses_2019 = df["Prepaid expenses"]["September 2019"]
prepaid_expenses_2018 = df["Prepaid expenses"]["September 2018"]
answer = (prepaid_expenses_2019 - prepaid_expenses_2018) / prepaid_expenses_2018 * 100.0