baker hughes , a ge company notes to consolidated and combined financial statements bhge 2017 form 10-k | 83 issuance pursuant to awards granted under the lti plan over its term which expires on the date of the annual meeting of the company in 2027 . a total of 53.7 million shares of class a common stock are available for issuance as of december 31 , 2017 . as a result of the acquisition of baker hughes , on july 3 , 2017 , each outstanding baker hughes stock option was converted into an option to purchase a share of class a common stock in the company . consequently , we issued 6.8 million stock options which are fully vested . each converted option is subject to the same terms and conditions as applied to the original option , and the per share exercise price of each converted option was reduced by $ 17.50 to reflect the per share amount of the special dividend pursuant to the agreement associated with the transactions . additionally , as a result of the acquisition of baker hughes , there were 1.7 million baker hughes restricted stock units ( rsus ) that were converted to bhge rsus at a fair value of $ 40.18 . stock-based compensation cost is measured at the date of grant based on the calculated fair value of the award and is generally recognized on a straight-line basis over the vesting period of the equity grant . the compensation cost is determined based on awards ultimately expected to vest ; therefore , we have reduced the cost for estimated forfeitures based on historical forfeiture rates . forfeitures are estimated at the time of grant and revised , if necessary , in subsequent periods to reflect actual forfeitures . there were no stock-based compensation costs capitalized as the amounts were not material . during the year ended december 31 , 2017 , we issued 2.1 million rsus and 1.6 million stock options under the lti plan . these rsus and stock options generally vest in equal amounts over a three-year vesting period provided that the employee has remained continuously employed by the company through such vesting date . stock based compensation expense was $ 37 million in 2017 . included in this amount is $ 15 million of expense which relates to the acceleration of equity awards upon termination of employment of baker hughes employees with change in control agreements , and are included as part of "merger and related costs" in the consolidated and combined statements of income ( loss ) . as bhge llc is a pass through entity , any tax benefit would be recognized by its partners . due to its cumulative losses , bhge is unable to recognize a tax benefit on its share of stock related expenses . stock options the fair value of each stock option granted is estimated using the black-scholes option pricing model . the following table presents the weighted average assumptions used in the option pricing model for options granted under the lti plan . the expected life of the options represents the period of time the options are expected to be outstanding . the expected life is based on a simple average of the vesting term and original contractual term of the awards . the expected volatility is based on the historical volatility of our five main competitors over a six year period . the risk-free interest rate is based on the observed u.s . treasury yield curve in effect at the time the options were granted . the dividend yield is based on a five year history of dividend payouts in baker hughes. .
what portion of the compensation expense in 2017 is relates to the acceleration of equity awards upon termination of employment at baker hughes?
.