What is the percentage change in product costs between 2018 and 2019?
{"Net revenues -- Product sales": {"$1,975": 1975, "$2,255": 2255}, "Net revenues -- Subscription, licensing, and other revenues": {"$1,975": 4514, "$2,255": 5245}, "Net revenues -- Total net revenues": {"$1,975": 6489, "$2,255": 7500}, "Cost of revenuesproduct sales: -- Product costs": {"$1,975": 656, "$2,255": 719}, "Cost of revenuesproduct sales: -- Software royalties, amortization, and intellectual property licenses": {"$1,975": 240, "$2,255": 371}, "Cost of revenuessubscription, licensing, and other -- Game operations and distribution costs": {"$1,975": 965, "$2,255": 1028}, "Cost of revenuessubscription, licensing, and other -- Software royalties, amortization, and intellectual property licenses": {"$1,975": 233, "$2,255": 399}, "Cost of revenuessubscription, licensing, and other -- Product development": {"$1,975": 998, "$2,255": 1101}, "Cost of revenuessubscription, licensing, and other -- Sales and marketing": {"$1,975": 926, "$2,255": 1062}, "Cost of revenuessubscription, licensing, and other -- General and administrative": {"$1,975": 732, "$2,255": 822}, "Cost of revenuessubscription, licensing, and other -- Restructuring and related costs": {"$1,975": 132, "$2,255": 10}, "Cost of revenuessubscription, licensing, and other -- Total costs and expenses": {"$1,975": 4882, "$2,255": 5512}, "Cost of revenuessubscription, licensing, and other -- Operating income": {"$1,975": 1607, "$2,255": 1988}, "Cost of revenuessubscription, licensing, and other -- Interest and other expense (income), net": {"$1,975": -26, "$2,255": 71}, "Cost of revenuessubscription, licensing, and other -- Loss on extinguishment of debt (2)": {"$1,975": "\u2014", "$2,255": 40}, "Cost of revenuessubscription, licensing, and other -- Income before income tax expense": {"$1,975": 1633, "$2,255": 1877}, "Cost of revenuessubscription, licensing, and other -- Income tax expense": {"$1,975": 130, "$2,255": 29}, "Cost of revenuessubscription, licensing, and other -- Net income": {"$1,975": 1503, "$2,255": 1848}}
product_costs_2019 = df["Cost of revenuesproduct sales: -- Product costs"]["$1,975"]
product_costs_2018 = df["Cost of revenuesproduct sales: -- Product costs"]["$2,255"]
answer = ( product_costs_2019 - product_costs_2018 ) / product_costs_2018 * 100.0