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% ( 30 % )', '27% ( 27 % )', '28% ( 28 % )'], ['risk-free interest rate', '3.1% ( 3.1 % )', '4.1% ( 4.1 % )', '5.0% ( 5.0 % )'], ['weighted average grant date fair value of stock option awards granted', '$ 13.03', '$ 17.24', '$ 10.19']]
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Question: by what percentage did the company's weighted average exercise price per share increase from 2006 to 2008?
Answer: 36.7%