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                                             | 2016         | 2015         |
|:-------------------------------------------------------|:-------------|:-------------|
| vehicles                                               | $ 68         | $ 74         |
| aircraft                                               | 2291         | 2289         |
| buildings                                              | 190          | 207          |
| accumulated amortization                               | -896 ( 896 ) | -849 ( 849 ) |
| property plant and equipment subject to capital leases | $ 1653       | $ 1721       |

Question:
what was the change in millions of vehicles from 2015 to 2016?


pre_text: united parcel service , inc .
and subsidiaries notes to consolidated financial statements 8.375% ( 8.375 % ) debentures the 8.375% ( 8.375 % ) debentures consist of two separate tranches , as follows : 2022 $ 276 million of the debentures have a maturity of april 1 , 2030 .
these debentures have an 8.375% ( 8.375 % ) interest rate until april 1 , 2020 , and , thereafter , the interest rate will be 7.62% ( 7.62 % ) for the final 10 years .
these debentures are redeemable in whole or in part at our option at any time .
the redemption price is equal to the greater of 100% ( 100 % ) of the principal amount and accrued interest , or the sum of the present values of the remaining scheduled payout of principal and interest thereon discounted to the date of redemption ( at a benchmark treasury yield plus five basis points ) plus accrued interest .
2022 $ 424 million of the debentures have a maturity of april 1 , 2020 .
these debentures are not subject to redemption prior to maturity .
interest is payable semiannually in april and october for both tranches and neither tranche is subject to sinking fund requirements .
we subsequently entered into interest rate swaps on the 2020 debentures , which effectively converted the fixed interest rates on the debentures to variable libor-based interest rates .
the average interest rate payable on the 2020 debentures , including the impact of the interest rate swaps , for 2016 and 2015 was 5.43% ( 5.43 % ) and 5.04% ( 5.04 % ) , respectively .
floating rate senior notes the floating rate senior notes bear interest at either one or three-month libor , less a spread ranging from 30 to 45 basis points .
the average interest rate for 2016 and 2015 was 0.21% ( 0.21 % ) and 0.01% ( 0.01 % ) , respectively .
these notes are callable at various times after 30 years at a stated percentage of par value , and putable by the note holders at various times after 10 years at a stated percentage of par value .
the notes have maturities ranging from 2049 through 2066 .
in march , june and august 2016 , we issued floating rate senior notes in principal balances of $ 118 , $ 74 and $ 35 million , respectively .
these notes bear interest at three-month libor less 30 basis points and mature in 2066 .
capital lease obligations we have certain property , plant and equipment subject to capital leases .
some of the obligations associated with these capital leases have been legally defeased .
the recorded value of our property , plant and equipment subject to capital leases is as follows as of december 31 ( in millions ) : .
post_text: these capital lease obligations have principal payments due at various dates from 2017 through 3005. .
label: -6
qa: answer: -6
ann_table_rows: 1
steps: op: minus1-1
arg1: 68
arg2: 74
res: -6
program: subtract(68, 74)
gold_inds: table_1: the vehicles of 2016 is $ 68 ; the vehicles of 2015 is $ 74 ;
exe_ans: -6
tfidftopn: text_18: the recorded value of our property , plant and equipment subject to capital leases is as follows as of december 31 ( in millions ) : .
table_2: The aircraft of 2016 is 2291 ; The aircraft of 2015 is 2289 ;
program_re: subtract(68, 74)
model_input: text_18
the recorded value of our property , plant and equipment subject to capital leases is as follows as of december 31 ( in millions ) : .
table_1
the vehicles of 2016 is $ 68 ; the vehicles of 2015 is $ 74 ;
table_5
the property plant and equipment subject to capital leases of 2016 is $ 1653 ; the property plant and equipment subject to capital leases of 2015 is $ 1721 ;