supplementary information on oil and gas producing activities ( unaudited ) 2017 proved reserves decreased by 647 mmboe primarily due to the following : 2022 revisions of previous estimates : increased by 49 mmboe primarily due to the acceleration of higher economic wells in the bakken into the 5-year plan resulting in an increase of 44 mmboe , with the remainder being due to revisions across the business .
2022 extensions , discoveries , and other additions : increased by 116 mmboe primarily due to an increase of 97 mmboe associated with the expansion of proved areas and wells to sales from unproved categories in oklahoma .
2022 purchases of reserves in place : increased by 28 mmboe from acquisitions of assets in the northern delaware basin in new mexico .
2022 production : decreased by 145 mmboe .
2022 sales of reserves in place : decreased by 695 mmboe including 685 mmboe associated with the sale of our canadian business and 10 mmboe associated with divestitures of certain conventional assets in oklahoma and colorado .
see item 8 .
financial statements and supplementary data - note 5 to the consolidated financial statements for information regarding these dispositions .
2016 proved reserves decreased by 67 mmboe primarily due to the following : 2022 revisions of previous estimates : increased by 63 mmboe primarily due to an increase of 151 mmboe associated with the acceleration of higher economic wells in the u.s .
resource plays into the 5-year plan and a decrease of 64 mmboe due to u.s .
technical revisions .
2022 extensions , discoveries , and other additions : increased by 60 mmboe primarily associated with the expansion of proved areas and new wells to sales from unproven categories in oklahoma .
2022 purchases of reserves in place : increased by 34 mmboe from acquisition of stack assets in oklahoma .
2022 production : decreased by 144 mmboe .
2022 sales of reserves in place : decreased by 84 mmboe associated with the divestitures of certain wyoming and gulf of mexico assets .
2015 proved reserves decreased by 35 mmboe primarily due to the following : 2022 revisions of previous estimates : decreased by 2 mmboe primarily resulting from an increase of 105 mmboe associated with drilling programs in u.s .
resource plays and an increase of 67 mmboe in discontinued operations due to technical reevaluation and lower royalty percentages related to lower realized prices , offset by a decrease of 173 mmboe which was largely due to reductions to our capital development program and adherence to the sec 5-year rule .
2022 extensions , discoveries , and other additions : increased by140 mmboe as a result of drilling programs in our u.s .
resource plays .
2022 production : decreased by 157 mmboe .
2022 sales of reserves in place : u.s .
conventional assets sales contributed to a decrease of 18 mmboe .
changes in proved undeveloped reserves as of december 31 , 2017 , 546 mmboe of proved undeveloped reserves were reported , a decrease of 6 mmboe from december 31 , 2016 .
the following table shows changes in proved undeveloped reserves for 2017 : ( mmboe ) .

Beginning of year
552
Revisions of previous estimates
5
Improved recovery
—
Purchases of reserves in place
15
Extensions, discoveries, and other additions
57
Dispositions
—
Transfers to proved developed
(83)
End of year
546

revisions of prior estimates .
revisions of prior estimates increased 5 mmboe during 2017 , primarily due to a 44 mmboe increase in the bakken from an acceleration of higher economic wells into the 5-year plan , offset by a decrease of 40 mmboe in oklahoma due to the removal of less economic wells from the 5-year plan .
extensions , discoveries and other additions .
increased 57 mmboe through expansion of proved areas in oklahoma. .

Question: Analyse this data from a financial earnings document. what was purchases of reserves in place in 2016?
Choices:
-10
7
-28
-13.0
13
Correct choice index: 3