marathon oil corporation notes to consolidated financial statements operating lease rental expense was : ( in millions ) 2008 2007 2006 minimum rental ( a ) $ 245 $ 209 $ 172 .

<i>(In millions)</i>
2008
2007
2006
Minimum rental<sup>(a)</sup>
$245
$209
$172
Contingent rental
22
33
28
Sublease rentals
–
–
(7)
Net rental expense
$267
$242
$193

( a ) excludes $ 5 million , $ 8 million and $ 9 million paid by united states steel in 2008 , 2007 and 2006 on assumed leases .
27 .
contingencies and commitments we are the subject of , or party to , a number of pending or threatened legal actions , contingencies and commitments involving a variety of matters , including laws and regulations relating to the environment .
certain of these matters are discussed below .
the ultimate resolution of these contingencies could , individually or in the aggregate , be material to our consolidated financial statements .
however , management believes that we will remain a viable and competitive enterprise even though it is possible that these contingencies could be resolved unfavorably .
environmental matters 2013 we are subject to federal , state , local and foreign laws and regulations relating to the environment .
these laws generally provide for control of pollutants released into the environment and require responsible parties to undertake remediation of hazardous waste disposal sites .
penalties may be imposed for noncompliance .
at december 31 , 2008 and 2007 , accrued liabilities for remediation totaled $ 111 million and $ 108 million .
it is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties that may be imposed .
receivables for recoverable costs from certain states , under programs to assist companies in clean-up efforts related to underground storage tanks at retail marketing outlets , were $ 60 and $ 66 million at december 31 , 2008 and 2007 .
we are a defendant , along with other refining companies , in 20 cases arising in three states alleging damages for methyl tertiary-butyl ether ( 201cmtbe 201d ) contamination .
we have also received seven toxic substances control act notice letters involving potential claims in two states .
such notice letters are often followed by litigation .
like the cases that were settled in 2008 , the remaining mtbe cases are consolidated in a multidistrict litigation in the southern district of new york for pretrial proceedings .
nineteen of the remaining cases allege damages to water supply wells , similar to the damages claimed in the settled cases .
in the other remaining case , the state of new jersey is seeking natural resources damages allegedly resulting from contamination of groundwater by mtbe .
this is the only mtbe contamination case in which we are a defendant and natural resources damages are sought .
we are vigorously defending these cases .
we , along with a number of other defendants , have engaged in settlement discussions related to the majority of the cases in which we are a defendant .
we do not expect our share of liability , if any , for the remaining cases to significantly impact our consolidated results of operations , financial position or cash flows .
a lawsuit filed in the united states district court for the southern district of west virginia alleges that our catlettsburg , kentucky , refinery distributed contaminated gasoline to wholesalers and retailers for a period prior to august , 2003 , causing permanent damage to storage tanks , dispensers and related equipment , resulting in lost profits , business disruption and personal and real property damages .
following the incident , we conducted remediation operations at affected facilities , and we deny that any permanent damages resulted from the incident .
class action certification was granted in august 2007 .
we have entered into a tentative settlement agreement in this case .
notice of the proposed settlement has been sent to the class members .
approval by the court after a fairness hearing is required before the settlement can be finalized .
the fairness hearing is scheduled in the first quarter of 2009 .
the proposed settlement will not significantly impact our consolidated results of operations , financial position or cash flows .
guarantees 2013 we have provided certain guarantees , direct and indirect , of the indebtedness of other companies .
under the terms of most of these guarantee arrangements , we would be required to perform should the guaranteed party fail to fulfill its obligations under the specified arrangements .
in addition to these financial guarantees , we also have various performance guarantees related to specific agreements. .

Question: Analyse this data from a financial earnings document. by how much did minimum rental increase from 2006 to 2008?
Choices:
2.35616
73
0.00424
9.125
0.42442
Correct choice index: 4