What is the ratio of gross deferred tax to net deferred tax liabilities on December 31, 2018?
{"December 31, -- ": {"2019": 2019, "2018": 2018}, "December 31, -- Goodwill and other intangibles": {"2019": 136882, "2018": 114532}, "December 31, -- Lease arrangements": {"2019": 31128, "2018": "\u2014"}, "December 31, -- Property and equipment": {"2019": 13270, "2018": 8168}, "December 31, -- Unbilled receivables - IRC Section 481(a)": {"2019": 5878, "2018": 8816}, "December 31, -- Gross deferred tax liabilities": {"2019": 187158, "2018": 131516}, "December 31, -- Lease obligations": {"2019": -34146, "2018": "\u2014"}, "December 31, -- Retirement and other liabilities": {"2019": -18614, "2018": -20707}, "December 31, -- Allowance for potential contract losses and other contract reserves": {"2019": -2205, "2018": -1681}, "December 31, -- Foreign and state operating loss carryforwards": {"2019": -2239, "2018": -1709}, "December 31, -- Less: Valuation allowance": {"2019": 1828, "2018": 1537}, "December 31, -- Gross deferred tax assets": {"2019": -55376, "2018": -22560}, "December 31, -- Net deferred tax liabilities": {"2019": 131782, "2018": 108956}}
gross_deferred_tax_2018 = df["December 31, -- Gross deferred tax liabilities"]["2018"]
net_deferred_tax_2018 = df["December 31, -- Net deferred tax liabilities"]["2018"]
answer = gross_deferred_tax_2018 / net_deferred_tax_2018