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                 | 2015                 | 2014                 | 2013                                   |
|:---------------------------|:---------------------|:---------------------|:---------------------------------------|
| grant-date fair value      | $ 81.99 2013 $ 85.05 | $ 70.18 2013 $ 81.05 | $ 61.27 2013 $ 63.48                   |
| risk-free interest rate    | 1.06% ( 1.06 % )     | 0.54% ( 0.54 % )     | 0.26% ( 0.26 % ) 2013 0.36% ( 0.36 % ) |
| volatility factor          | 26.2% ( 26.2 % )     | 28.8% ( 28.8 % )     | 30.3% ( 30.3 % )                       |
| contractual term ( years ) | 2.89                 | 2.89                 | 3.0                                    |

Question:
in years , what is the average contractual term for 2013 , 2014 , 2015?


pre_text: devon energy corporation and subsidiaries notes to consolidated financial statements 2013 ( continued ) restricted stock awards and units restricted stock awards and units are subject to the terms , conditions , restrictions and limitations , if any , that the compensation committee deems appropriate , including restrictions on continued employment .
generally , the service requirement for vesting ranges from zero to four years .
during the vesting period , recipients of restricted stock awards receive dividends that are not subject to restrictions or other limitations .
devon estimates the fair values of restricted stock awards and units as the closing price of devon 2019s common stock on the grant date of the award or unit , which is expensed over the applicable vesting period .
performance-based restricted stock awards performance-based restricted stock awards are granted to certain members of devon 2019s senior management .
vesting of the awards is dependent on devon meeting certain internal performance targets and the recipient meeting certain service requirements .
generally , the service requirement for vesting ranges from zero to four years .
in order for awards to vest , the performance target must be met in the first year , and if met , recipients are entitled to dividends on the awards over the remaining service vesting period .
if the performance target and service period requirements are not met , the award does not vest .
devon estimates the fair values of the awards as the closing price of devon 2019s common stock on the grant date of the award , which is expensed over the applicable vesting period .
performance share units performance share units are granted to certain members of devon 2019s senior management .
each unit that vests entitles the recipient to one share of devon common stock .
the vesting of these units is based on comparing devon 2019s tsr to the tsr of a predetermined group of fourteen peer companies over the specified two- or three- year performance period .
the vesting of units may be between zero and 200% ( 200 % ) of the units granted depending on devon 2019s tsr as compared to the peer group on the vesting date .
at the end of the vesting period , recipients receive dividend equivalents with respect to the number of units vested .
the fair value of each performance share unit is estimated as of the date of grant using a monte carlo simulation with the following assumptions used for all grants made under the plan : ( i ) a risk-free interest rate based on u.s .
treasury rates as of the grant date ; ( ii ) a volatility assumption based on the historical realized price volatility of devon and the designated peer group ; and ( iii ) an estimated ranking of devon among the designated peer group .
the fair value of the unit on the date of grant is expensed over the applicable vesting period .
the following table presents the assumptions related to performance share units granted. .
post_text: stock options in accordance with devon 2019s incentive plans , the exercise price of stock options granted may not be less than the market value of the stock at the date of grant .
in addition , options granted are exercisable during a period established for each grant , which may not exceed eight years from the date of grant .
the recipient must pay the exercise price in cash or in common stock , or a combination thereof , at the time that the option is exercised .
generally , the service requirement for vesting ranges from zero to four years .
the fair value of stock options on .
label: 2.92667
qa: answer: 2.9266
ann_table_rows: 4
ann_text_rows: 18
steps: op: add2-1
arg1: 2.89
arg2: 2.89
res: 5.78
op: add2-2
arg1: #0
arg2: const_3
res: 8.78
op: divide2-3
arg1: #1
arg2: const_3
res: 2.9266
program: add(2.89, 2.89), add(#0, const_3), divide(#1, const_3)
gold_inds: table_4: the contractual term ( years ) of 2015 is 2.89 ; the contractual term ( years ) of 2014 is 2.89 ; the contractual term ( years ) of 2013 is 3.0 ;
text_18: the following table presents the assumptions related to performance share units granted. .
exe_ans: 2.92667
tfidftopn: table_1: The grant-date fair value of 2015 is $ 81.99 2013 $ 85.05 ; The grant-date fair value of 2014 is $ 70.18 2013 $ 81.05 ; The grant-date fair value of 2013 is $ 61.27 2013 $ 63.48 ;
program_re: divide(add(add(2.89, 2.89), const_3), const_3)
model_input: text_18
the following table presents the assumptions related to performance share units granted. .
table_1
the grant-date fair value of 2015 is $ 81.99 2013 $ 85.05 ; the grant-date fair value of 2014 is $ 70.18 2013 $ 81.05 ; the grant-date fair value of 2013 is $ 61.27 2013 $ 63.48 ;
table_4
the contractual term ( years ) of 2015 is 2.89 ; the contractual term ( years ) of 2014 is 2.89 ; the contractual term ( years ) of 2013 is 3.0 ;