What was the percentage change in amounts charged to cost and expenses between 2017 and 2018?
{"Balance at beginning of period": {"2019": 8623, "2018": 9724, "2017": 8548}, "Plus: Amounts charged to cost and expenses": {"2019": 4569, "2018": 7392, "2017": 6951}, "Less: Deductions": {"2019": -4798, "2018": -8493, "2017": -5775}, "Balance at end of period": {"2019": 8394, "2018": 8623, "2017": 9724}}
amounts_2018 = df["Plus: Amounts charged to cost and expenses"]["2018"]
amounts_2017 = df["Plus: Amounts charged to cost and expenses"]["2017"]
answer = (amounts_2018 - amounts_2017) / amounts_2017 * 100.0