failure to comply with the financial and other covenants under our credit facilities , as well as the occurrence of certain material adverse events , would constitute defaults and would allow the lenders under our credit facilities to accelerate the maturity of all indebtedness under the related agreements . this could also have an adverse impact on the availability of financial assurances . in addition , maturity acceleration on our credit facilities constitutes an event of default under our other debt instruments , including our senior notes , and , therefore , our senior notes would also be subject to acceleration of maturity . if such acceleration were to occur , we would not have sufficient liquidity available to repay the indebtedness . we would likely have to seek an amendment under our credit facilities for relief from the financial covenants or repay the debt with proceeds from the issuance of new debt or equity , or asset sales , if necessary . we may be unable to amend our credit facilities or raise sufficient capital to repay such obligations in the event the maturities are accelerated . financial assurance we are required to provide financial assurance to governmental agencies and a variety of other entities under applicable environmental regulations relating to our landfill operations for capping , closure and post-closure costs , and related to our performance under certain collection , landfill and transfer station contracts . we satisfy these financial assurance requirements by providing surety bonds , letters of credit , insurance policies or trust deposits . the amount of the financial assurance requirements for capping , closure and post-closure costs is determined by applicable state environmental regulations . the financial assurance requirements for capping , closure and post-closure costs may be associated with a portion of the landfill or the entire landfill . generally , states will require a third-party engineering specialist to determine the estimated capping , closure and post- closure costs that are used to determine the required amount of financial assurance for a landfill . the amount of financial assurance required can , and generally will , differ from the obligation determined and recorded under u.s . gaap . the amount of the financial assurance requirements related to contract performance varies by contract . additionally , we are required to provide financial assurance for our insurance program and collateral for certain performance obligations . we do not expect a material increase in financial assurance requirements during 2010 , although the mix of financial assurance instruments may change . these financial instruments are issued in the normal course of business and are not debt of our company . since we currently have no liability for these financial assurance instruments , they are not reflected in our consolidated balance sheets . however , we record capping , closure and post-closure liabilities and self-insurance liabilities as they are incurred . the underlying obligations of the financial assurance instruments , in excess of those already reflected in our consolidated balance sheets , would be recorded if it is probable that we would be unable to fulfill our related obligations . we do not expect this to occur . off-balance sheet arrangements we have no off-balance sheet debt or similar obligations , other than financial assurance instruments and operating leases that are not classified as debt . we do not guarantee any third-party debt . free cash flow we define free cash flow , which is not a measure determined in accordance with u.s . gaap , as cash provided by operating activities less purchases of property and equipment , plus proceeds from sales of property and equipment as presented in our consolidated statements of cash flows . our free cash flow for the years ended december 31 , 2009 , 2008 and 2007 is calculated as follows ( in millions ) : .

2009: cash provided by operating activities: 1396.5
purchases of property and equipment: -826.3
proceeds from sales of property and equipment: 31.8
free cash flow: 602
2008: cash provided by operating activities: 512.2
purchases of property and equipment: -386.9
proceeds from sales of property and equipment: 8.2
free cash flow: 133.5
2007: cash provided by operating activities: 661.3
purchases of property and equipment: -292.5
proceeds from sales of property and equipment: 6.1
free cash flow: 374.9

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Questions:
what is the cash provided by operating activities of 2008?
and that of 2007?
what is the difference between the cash provided by operating activities of 2008 and 2007?
how much does that difference represents in relation to the cash provided by operating activities of 2007?

Answers:
512.2
661.3
-149.1
-23%