zimmer biomet holdings , inc .
2015 form 10-k annual report notes to consolidated financial statements ( continued ) these unaudited pro forma results have been prepared for comparative purposes only and include adjustments such as inventory step-up , amortization of acquired intangible assets and interest expense on debt incurred to finance the merger .
material , nonrecurring pro forma adjustments directly attributable to the biomet merger include : 2022 the $ 90.4 million of merger compensation expense for unvested lvb stock options and lvb stock-based awards was removed from net earnings for the year ended december 31 , 2015 and recognized as an expense in the year ended december 31 , 2014 .
2022 the $ 73.0 million of retention plan expense was removed from net earnings for the year ended december 31 , 2015 and recognized as an expense in the year ended december 31 , 2014 .
2022 transaction costs of $ 17.7 million was removed from net earnings for the year ended december 31 , 2015 and recognized as an expense in the year ended december 31 , other acquisitions we made a number of business acquisitions during the years 2014 and 2013 .
in october 2014 , we acquired etex holdings , inc .
( 201cetex 201d ) .
the etex acquisition enhanced our biologics portfolio through the addition of etex 2019s bone void filler products .
in may 2013 , we acquired the business assets of knee creations , llc ( 201cknee creations 201d ) .
the knee creations acquisition enhanced our product portfolio of joint preservation solutions .
in june 2013 , we acquired normed medizin-technik gmbh ( 201cnormed 201d ) .
the normed acquisition strengthened our extremities and trauma product portfolios and brought new product development capabilities in the foot and ankle and hand and wrist markets .
the results of operations of these acquired companies have been included in our consolidated results of operations subsequent to the transaction dates , and the respective assets and liabilities of the acquired companies have been recorded at their estimated fair values in our consolidated statement of financial position as of the transaction dates , with any excess purchase price being recorded as goodwill .
pro forma financial information and other information required by gaap have not been included for these acquisitions as they , individually and in the aggregate , did not have a material impact upon our financial position or results of operations .
5 .
share-based compensation our share-based payments primarily consist of stock options and restricted stock units ( 201crsus 201d ) .
share-based compensation expense was as follows ( in millions ) : .

For the Years Ended December 31,
2015
2014
2013
Total expense, pre-tax
$46.4
$49.4
$48.5
Tax benefit related to awards
(14.5)
(15.5)
(15.6)
Total expense, net of tax
$31.9
$33.9
$32.9

stock options we had two equity compensation plans in effect at december 31 , 2015 : the 2009 stock incentive plan ( 201c2009 plan 201d ) and the stock plan for non-employee directors .
the 2009 plan succeeded the 2006 stock incentive plan ( 201c2006 plan 201d ) and the teamshare stock option plan ( 201cteamshare plan 201d ) .
no further awards have been granted under the 2006 plan or under the teamshare plan since may 2009 , and shares remaining available for grant under those plans have been merged into the 2009 plan .
vested stock options previously granted under the 2006 plan , the teamshare plan and another prior plan , the 2001 stock incentive plan , remained outstanding as of december 31 , 2015 .
we have reserved the maximum number of shares of common stock available for award under the terms of each of these plans .
we have registered 57.9 million shares of common stock under these plans .
the 2009 plan provides for the grant of nonqualified stock options and incentive stock options , long-term performance awards in the form of performance shares or units , restricted stock , rsus and stock appreciation rights .
the compensation and management development committee of the board of directors determines the grant date for annual grants under our equity compensation plans .
the date for annual grants under the 2009 plan to our executive officers is expected to occur in the first quarter of each year following the earnings announcements for the previous quarter and full year .
in 2015 , the compensation and management development committee set the closing date as the grant date for awards to our executive officers .
the stock plan for non-employee directors provides for awards of stock options , restricted stock and rsus to non-employee directors .
it has been our practice to issue shares of common stock upon exercise of stock options from previously unissued shares , except in limited circumstances where they are issued from treasury stock .
the total number of awards which may be granted in a given year and/or over the life of the plan under each of our equity compensation plans is limited .
at december 31 , 2015 , an aggregate of 5.6 million shares were available for future grants and awards under these plans .
stock options granted to date under our plans vest over four years and have a maximum contractual life of 10 years .
as established under our equity compensation plans , vesting may accelerate upon retirement after the first anniversary date of the award if certain criteria are met .
we recognize expense related to stock options on a straight-line basis over the requisite service period , less awards expected to be forfeited using estimated forfeiture rates .
due to the accelerated retirement provisions , the requisite service period of our stock options range from one to four years .
stock options are granted with an exercise price equal to the market price of our common stock on the date of grant , except in limited circumstances where local law may dictate otherwise. .

Question: Analyse this data from a financial earnings document. what was the change in total expense net of tax for share based compensation from 2013 to 2014 in millions?
Choices:
2
-12.9
1.0
-24
66.8
Correct choice index: 2