marathon oil corporation notes to consolidated financial statements stock appreciation rights 2013 prior to 2005 , we granted sars under the 2003 plan .
no stock appreciation rights have been granted under the 2007 plan .
similar to stock options , stock appreciation rights represent the right to receive a payment equal to the excess of the fair market value of shares of common stock on the date the right is exercised over the grant price .
under the 2003 plan , certain sars were granted as stock-settled sars and others were granted in tandem with stock options .
in general , sars granted under the 2003 plan vest ratably over a three-year period and have a maximum term of ten years from the date they are granted .
stock-based performance awards 2013 prior to 2005 , we granted stock-based performance awards under the 2003 plan .
no stock-based performance awards have been granted under the 2007 plan .
beginning in 2005 , we discontinued granting stock-based performance awards and instead now grant cash-settled performance units to officers .
all stock-based performance awards granted under the 2003 plan have either vested or been forfeited .
as a result , there are no outstanding stock-based performance awards .
restricted stock 2013 we grant restricted stock and restricted stock units under the 2007 plan and previously granted such awards under the 2003 plan .
in 2005 , the compensation committee began granting time-based restricted stock to certain u.s.-based officers of marathon and its consolidated subsidiaries as part of their annual long-term incentive package .
the restricted stock awards to officers vest three years from the date of grant , contingent on the recipient 2019s continued employment .
we also grant restricted stock to certain non-officer employees and restricted stock units to certain international employees ( 201crestricted stock awards 201d ) , based on their performance within certain guidelines and for retention purposes .
the restricted stock awards to non-officers generally vest in one-third increments over a three-year period , contingent on the recipient 2019s continued employment , however , certain restricted stock awards granted in 2008 will vest over a four-year period , contingent on the recipient 2019s continued employment .
prior to vesting , all restricted stock recipients have the right to vote such stock and receive dividends thereon .
the non-vested shares are not transferable and are held by our transfer agent .
common stock units 2013 we maintain an equity compensation program for our non-employee directors under the 2007 plan and previously maintained such a program under the 2003 plan .
all non-employee directors other than the chairman receive annual grants of common stock units , and they are required to hold those units until they leave the board of directors .
when dividends are paid on marathon common stock , directors receive dividend equivalents in the form of additional common stock units .
total stock-based compensation expense total employee stock-based compensation expense was $ 43 million , $ 66 million and $ 78 million in 2008 , 2007 and 2006 .
the total related income tax benefits were $ 16 million , $ 24 million and $ 29 million .
in 2008 and 2007 , cash received upon exercise of stock option awards was $ 9 million and $ 27 million .
tax benefits realized for deductions during 2008 and 2007 that were in excess of the stock-based compensation expense recorded for options exercised and other stock-based awards vested during the period totaled $ 7 million and $ 30 million .
cash settlements of stock option awards totaled $ 1 million in 2007 .
there were no cash settlements in 2008 .
stock option awards during 2008 , 2007 and 2006 , we granted stock option awards to both officer and non-officer employees .
the weighted average grant date fair value of these awards was based on the following black-scholes assumptions: .

2008
2007
2006
Weighted average exercise price per share
$51.74
$60.94
$37.84
Expected annual dividends per share
$0.96
$0.96
$0.80
Expected life in years
4.8
5.0
5.1
Expected volatility
30%
27%
28%
Risk-free interest rate
3.1%
4.1%
5.0%
Weighted average grant date fair value of stock option awards granted
$13.03
$17.24
$10.19

.

Question: Analyse this data from a financial earnings document. by what percentage did the company's weighted average exercise price per share increase from 2006 to 2008?
Choices:
-0.36734
0.22809
0.26865
0.36734
0.13636
Correct choice index: 3