{"pre_text": ["american tower corporation and subsidiaries notes to consolidated financial statements 2014 ( continued ) from december 1 through may 31 of each year .", "during the 2008 , 2007 and 2006 offering periods employees purchased 55764 , 48886 and 53210 shares , respectively , at weighted average prices per share of $ 30.08 , $ 33.93 and $ 24.98 , respectively .", "the fair value of the espp offerings is estimated on the offering period commencement date using a black-scholes pricing model with the expense recognized over the expected life , which is the six month offering period over which employees accumulate payroll deductions to purchase the company 2019s common stock .", "the weighted average fair value for the espp shares purchased during 2008 , 2007 and 2006 were $ 7.89 , $ 9.09 and $ 6.79 , respectively .", "at december 31 , 2008 , 8.8 million shares remain reserved for future issuance under the plan .", "key assumptions used to apply this pricing model for the years ended december 31 , are as follows: ."], "post_text": ["13 .", "stockholders 2019 equity warrants 2014in january 2003 , the company issued warrants to purchase approximately 11.4 million shares of its common stock in connection with an offering of 808000 units , each consisting of $ 1000 principal amount at maturity of ati 12.25% ( 12.25 % ) senior subordinated discount notes due 2008 and a warrant to purchase 14.0953 shares of the company 2019s common stock .", "these warrants became exercisable on january 29 , 2006 at an exercise price of $ 0.01 per share .", "as these warrants expired on august 1 , 2008 , none were outstanding as of december 31 , in august 2005 , the company completed its merger with spectrasite , inc .", "and assumed outstanding warrants to purchase shares of spectrasite , inc .", "common stock .", "as of the merger completion date , each warrant was exercisable for two shares of spectrasite , inc .", "common stock at an exercise price of $ 32 per warrant .", "upon completion of the merger , each warrant to purchase shares of spectrasite , inc .", "common stock automatically converted into a warrant to purchase shares of the company 2019s common stock , such that upon exercise of each warrant , the holder has a right to receive 3.575 shares of the company 2019s common stock in lieu of each share of spectrasite , inc .", "common stock that would have been receivable under each assumed warrant prior to the merger .", "upon completion of the company 2019s merger with spectrasite , inc. , these warrants were exercisable for approximately 6.8 million shares of common stock .", "of these warrants , warrants to purchase approximately 1.8 million and 2.0 million shares of common stock remained outstanding as of december 31 , 2008 and 2007 , respectively .", "these warrants will expire on february 10 , 2010 .", "stock repurchase programs 2014during the year ended december 31 , 2008 , the company repurchased an aggregate of approximately 18.3 million shares of its common stock for an aggregate of $ 697.1 million , including commissions and fees , pursuant to its publicly announced stock repurchase programs , as described below. ."], "table": [["", "2008", "2007", "2006"], ["range of risk free interest rates", "1.99% ( 1.99 % ) 20143.28% ( 20143.28 % )", "4.98% ( 4.98 % ) 20145.05% ( 20145.05 % )", "5.01% ( 5.01 % ) 20145.17% ( 20145.17 % )"], ["weighted average risk-free interest rate", "2.58% ( 2.58 % )", "5.02% ( 5.02 % )", "5.08% ( 5.08 % )"], ["expected life of the shares", "6 months", "6 months", "6 months"], ["range of expected volatility of underlying stock price", "27.85% ( 27.85 % ) 201428.51% ( 201428.51 % )", "27.53% ( 27.53 % ) 201428.74% ( 201428.74 % )", "29.60% ( 29.60 % )"], ["weighted average expected volatility of underlying stock price", "28.51% ( 28.51 % )", "28.22% ( 28.22 % )", "29.60% ( 29.60 % )"], ["expected annual dividends", "n/a", "n/a", "n/a"]], "table_ori": [["", "2008", "2007", "2006"], ["Range of risk free interest rates", "1.99%—3.28%", "4.98%—5.05%", "5.01%—5.17%"], ["Weighted average risk-free interest rate", "2.58%", "5.02%", "5.08%"], ["Expected life of the shares", "6 months", "6 months", "6 months"], ["Range of expected volatility of underlying stock price", "27.85%—28.51%", "27.53%—28.74%", "29.60%"], ["Weighted average expected volatility of underlying stock price", "28.51%", "28.22%", "29.60%"], ["Expected annual dividends", "N/A", "N/A", "N/A"]]}

Question: what was the percentage change in the weighted average risk-free interest rate from 2007 to 2008
Evidence:
table_2: the weighted average risk-free interest rate of 2008 is 2.58% ( 2.58 % ) ; the weighted average risk-free interest rate of 2007 is 5.02% ( 5.02 % ) ; the weighted average risk-free interest rate of 2006 is 5.08% ( 5.08 % ) ;
Program: subtract(2.58, 5.02), divide(#0, 5.02)
Answer:
str_answer: -48.6%
exe_answer: -0.48606