Task: Table-QA (source dataset: FinQA)

Task: 
You are given a table containing structured data and a natural language question referring to the table. Your goal is to analyze the table and provide an accurate and concise answer based on the given data.

Instructions:
1. Understand the Table: Examine the structure, headers, and data in the table. Identify relevant columns and rows related to the question.
2. Interpret the Question: Determine whether the question requires direct retrieval, aggregation, comparison, sorting, filtering, or inference.
3. Extract the Answer: Use logical reasoning and numerical operations (if necessary) to derive the correct response from the table.
4. Format the Answer: No explanation, return the answer in a structured JSON format: {"answer": <answer>}. If the question cannot be answered due to missing or ambiguous data, return a JSON response with {"answer": null}.

Table:
| Unnamed: 0                    | 2009             | 2008             | 2007             |
|:------------------------------|:-----------------|:-----------------|:-----------------|
| expected volatility           | 28.7% ( 28.7 % ) | 27.3% ( 27.3 % ) | 23.5% ( 23.5 % ) |
| risk-free interest rate       | 1.4% ( 1.4 % )   | 1.7% ( 1.7 % )   | 4.8% ( 4.8 % )   |
| dividend yield                | 3.1% ( 3.1 % )   | 2.9% ( 2.9 % )   | 1.5% ( 1.5 % )   |
| expected life ( in years )    | 4.2              | 4.2              | 4.0              |
| contractual life ( in years ) | 7                | 7                | 7                |
| expected forfeiture rate      | 3.0% ( 3.0 % )   | 3.0% ( 3.0 % )   | 5.0% ( 5.0 % )   |

Question:
what was the percentage decline in the weighted- average estimated fair values of stock options from 2007 to 2008


pre_text: awards .
awards granted under the 2006 plan prior to december 5 , 2008 became fully vested and nonforfeitable upon the closing of the merger .
awards may be granted under the 2006 plan , as amended and restated , after december 5 , 2008 only to employees and consultants of allied waste industries , inc .
and its subsidiaries who were not employed by republic services , inc .
prior to such date .
at december 31 , 2009 , there were approximately 15.3 million shares of common stock reserved for future grants under the 2006 plan .
stock options we use a lattice binomial option-pricing model to value our stock option grants .
we recognize compensation expense on a straight-line basis over the requisite service period for each separately vesting portion of the award , or to the employee 2019s retirement eligible date , if earlier .
expected volatility is based on the weighted average of the most recent one-year volatility and a historical rolling average volatility of our stock over the expected life of the option .
the risk-free interest rate is based on federal reserve rates in effect for bonds with maturity dates equal to the expected term of the option .
we use historical data to estimate future option exercises , forfeitures and expected life of the options .
when appropriate , separate groups of employees that have similar historical exercise behavior are considered separately for valuation purposes .
the weighted- average estimated fair values of stock options granted during the years ended december 31 , 2009 , 2008 and 2007 were $ 3.79 , $ 4.36 and $ 6.49 per option , respectively , which were calculated using the following weighted-average assumptions: .
post_text: republic services , inc .
and subsidiaries notes to consolidated financial statements , continued .
label: -0.3282
qa: answer: -32.8%
explanation: the weighted- average estimated fair values of stock options from 2007 to 2008 declined by 32.8%
ann_text_rows: 12
steps: op: minus2-1
arg1: 4.36
arg2: 6.49
res: -2.13
op: divide2-2
arg1: #0
arg2: 6.49
res: -32.8%
program: subtract(4.36, 6.49), divide(#0, 6.49)
gold_inds: text_12: the weighted- average estimated fair values of stock options granted during the years ended december 31 , 2009 , 2008 and 2007 were $ 3.79 , $ 4.36 and $ 6.49 per option , respectively , which were calculated using the following weighted-average assumptions: .
exe_ans: -0.3282
tfidftopn: text_8: expected volatility is based on the weighted average of the most recent one-year volatility and a historical rolling average volatility of our stock over the expected life of the option .
text_6: stock options we use a lattice binomial option-pricing model to value our stock option grants .
program_re: divide(subtract(4.36, 6.49), 6.49)
model_input: text_0
awards .
text_12
the weighted- average estimated fair values of stock options granted during the years ended december 31 , 2009 , 2008 and 2007 were $ 3.79 , $ 4.36 and $ 6.49 per option , respectively , which were calculated using the following weighted-average assumptions: .
text_14
and subsidiaries notes to consolidated financial statements , continued .