material impact on the service cost and interest cost components of net periodic benefit costs for a 1% ( 1 % ) change in the assumed health care trend rate .
for most of the participants in the u.s .
plan , aon 2019s liability for future plan cost increases for pre-65 and medical supplement plan coverage is limited to 5% ( 5 % ) per annum .
because of this cap , net employer trend rates for these plans are effectively limited to 5% ( 5 % ) per year in the future .
during 2007 , aon recognized a plan amendment which phases out post-65 retiree coverage in its u.s .
plan over the next three years .
the impact of this amendment on net periodic benefit cost is being recognized over the average remaining service life of the employees .
14 .
stock compensation plans the following table summarizes stock-based compensation expense recognized in continuing operations in the consolidated statements of income in compensation and benefits ( in millions ) : .

Years ended December 31
2010
2009
2008
RSUs
$138
$124
$132
Performance plans
62
60
67
Stock options
17
21
24
Employee stock purchase plans
4
4
3
Total stock-based compensation expense
221
209
226
Tax benefit
75
68
82
Stock-based compensation expense, net of tax
$146
$141
$144

during 2009 , the company converted its stock administration system to a new service provider .
in connection with this conversion , a reconciliation of the methodologies and estimates utilized was performed , which resulted in a $ 12 million reduction of expense for the year ended december 31 , 2009 .
stock awards stock awards , in the form of rsus , are granted to certain employees and consist of both performance-based and service-based rsus .
service-based awards generally vest between three and ten years from the date of grant .
the fair value of service-based awards is based upon the market value of the underlying common stock at the date of grant .
with certain limited exceptions , any break in continuous employment will cause the forfeiture of all unvested awards .
compensation expense associated with stock awards is recognized over the service period .
dividend equivalents are paid on certain service-based rsus , based on the initial grant amount .
performance-based rsus have been granted to certain employees .
vesting of these awards is contingent upon meeting various individual , divisional or company-wide performance conditions , including revenue generation or growth in revenue , pretax income or earnings per share over a one- to five-year period .
the performance conditions are not considered in the determination of the grant date fair value for these awards .
the fair value of performance-based awards is based upon the market price of the underlying common stock at the date of grant .
compensation expense is recognized over the performance period , and in certain cases an additional vesting period , based on management 2019s estimate of the number of units expected to vest .
compensation expense is adjusted to reflect the actual number of shares paid out at the end of the programs .
the actual payout of shares under these performance- based plans may range from 0-200% ( 0-200 % ) of the number of units granted , based on the plan .
dividend equivalents are generally not paid on the performance-based rsus .
during 2010 , the company granted approximately 1.6 million shares in connection with the completion of the 2007 leadership performance plan ( 2018 2018lpp 2019 2019 ) cycle and 84000 shares related to other performance plans .
during 2010 , 2009 and 2008 , the company granted approximately 3.5 million .

Question: Analyse this data from a financial earnings document. what was the average total stock-based compensation expense from 2008 to 2010 in millions
Choices:
10.1
327
329.5
335.5
659
Correct choice index: 2