Read the following texts and table with financial data from an S&P 500 earnings report carefully.Based on the question-answer history (if provided), answer the last question. The answer may require mathematical calculation based on the data provided.


notes to consolidated financial statements 2014 ( continued ) the weighted average grant-date fair value of share awards granted in the years ended may 31 , 2007 and 2006 was $ 45 and $ 36 , respectively . the total fair value of share awards vested during the years ended may 31 , 2008 , 2007 and 2006 was $ 4.1 million , $ 1.7 million and $ 1.4 million , respectively . we recognized compensation expenses for restricted stock of $ 5.7 million , $ 2.7 million , and $ 1.6 million in the years ended may 31 , 2008 , 2007 and 2006 . as of may 31 , 2008 , there was $ 15.2 million of total unrecognized compensation cost related to unvested restricted stock awards that is expected to be recognized over a weighted average period of 2.9 years . employee stock purchase plan we have an employee stock purchase plan under which the sale of 2.4 million shares of our common stock has been authorized . employees may designate up to the lesser of $ 25 thousand or 20% ( 20 % ) of their annual compensation for the purchase of stock . for periods prior to october 1 , 2006 , the price for shares purchased under the plan was the lower of 85% ( 85 % ) of the market value on the first day or the last day of the quarterly purchase period . with the quarterly purchase period beginning on october 1 , 2006 , the price for shares purchased under the plan is 85% ( 85 % ) of the market value on the last day of the quarterly purchase period ( the 201cpurchase date 201d ) . at may 31 , 2008 , 0.7 million shares had been issued under this plan , with 1.7 million shares reserved for future issuance . the weighted average grant-date fair value of each designated share purchased under this plan was $ 6 , $ 8 and $ 8 in the years ended may 31 , 2008 , 2007 and 2006 , respectively . for the quarterly purchases after october 1 , 2006 , the fair value of each designated share purchased under the employee stock purchase plan is based on the 15% ( 15 % ) discount on the purchase date . for purchases prior to october 1 , 2006 , the fair value of each designated share purchased under the employee stock purchase plan was estimated on the date of grant using the black-scholes valuation model using the following weighted average assumptions: . <table class='wikitable'><tr><td>1</td><td>-</td><td>2007</td><td>2006</td></tr><tr><td>2</td><td>risk-free interest rates</td><td>4.93% ( 4.93 % )</td><td>3.72% ( 3.72 % )</td></tr><tr><td>3</td><td>expected volatility</td><td>37.02% ( 37.02 % )</td><td>26.06% ( 26.06 % )</td></tr><tr><td>4</td><td>dividend yields</td><td>0.19% ( 0.19 % )</td><td>0.34% ( 0.34 % )</td></tr><tr><td>5</td><td>expected lives</td><td>3 months</td><td>3 months</td></tr></table> the risk-free interest rate is based on the yield of a zero coupon united states treasury security with a maturity equal to the expected life of the option from the date of the grant . our assumption on expected volatility is based on our historical volatility . the dividend yield assumption is calculated using our average stock price over the preceding year and the annualized amount of our current quarterly dividend . since the purchase price for shares under the plan is based on the market value on the first day or last day of the quarterly purchase period , we use an expected life of three months to determine the fair value of each designated share. .
Question: what was the difference in the weighted average grant-date fair value of share awards from 2006 to 2007?

9.0