what is the average balance of letters of credit outstanding as of december 31 , 2007 and 2006 , in millions?
page 59 of 94 notes to consolidated financial statements ball corporation and subsidiaries 13 . debt and interest costs ( continued ) long-term debt obligations outstanding at december 31 , 2007 , have maturities of $ 127.1 million , $ 160 million , $ 388.4 million , $ 625.1 million and $ 550.3 million for the years ending december 31 , 2008 through 2012 , respectively , and $ 456.1 million thereafter . ball provides letters of credit in the ordinary course of business to secure liabilities recorded in connection with industrial development revenue bonds and certain self-insurance arrangements . letters of credit outstanding at december 31 , 2007 and 2006 , were $ 41 million and $ 52.4 million , respectively . the notes payable and senior credit facilities are guaranteed on a full , unconditional and joint and several basis by certain of the company 2019s domestic wholly owned subsidiaries . certain foreign denominated tranches of the senior credit facilities are similarly guaranteed by certain of the company 2019s wholly owned foreign subsidiaries . note 22 contains further details as well as condensed , consolidating financial information for the company , segregating the guarantor subsidiaries and non-guarantor subsidiaries . the company was not in default of any loan agreement at december 31 , 2007 , and has met all debt payment obligations . the u.s . note agreements , bank credit agreement and industrial development revenue bond agreements contain certain restrictions relating to dividend payments , share repurchases , investments , financial ratios , guarantees and the incurrence of additional indebtedness . on march 27 , 2006 , ball expanded its senior secured credit facilities with the addition of a $ 500 million term d loan facility due in installments through october 2011 . also on march 27 , 2006 , ball issued at a price of 99.799 percent $ 450 million of 6.625% ( 6.625 % ) senior notes ( effective yield to maturity of 6.65 percent ) due in march 2018 . the proceeds from these financings were used to refinance existing u.s . can debt with ball corporation debt at lower interest rates , acquire certain north american plastic container net assets from alcan and reduce seasonal working capital debt . ( see note 3 for further details of the acquisitions. ) on october 13 , 2005 , ball refinanced its senior secured credit facilities to extend debt maturities at lower interest rate spreads and provide the company with additional borrowing capacity for future growth . during the third and fourth quarters of 2005 , ball redeemed its 7.75% ( 7.75 % ) senior notes due in august 2006 . the refinancing and senior note redemptions resulted in a debt refinancing charge of $ 19.3 million ( $ 12.3 million after tax ) for the related call premium and unamortized debt issuance costs . a summary of total interest cost paid and accrued follows: .

| ($ in millions) | 2007 | 2006 | 2005 |
| :--- | :--- | :--- | :--- |
| Interest costs before refinancing costs | $155.8 | $142.5 | $102.4 |
| Debt refinancing costs | – | – | 19.3 |
| Total interest costs | 155.8 | 142.5 | 121.7 |
| Amounts capitalized | (6.4) | (8.1) | (5.3) |
| Interest expense | $149.4 | $134.4 | $116.4 |
| Interest paid during the year(a) | $153.9 | $125.4 | $138.5 |

( a ) includes $ 6.6 million paid in 2005 in connection with the redemption of the company 2019s senior and senior subordinated notes. .

letters_of_credit_2007 = 41
letters_of_credit_2006 = 52.4
total_letters_of_credit = letters_of_credit_2007 + letters_of_credit_2006
average_letters_of_credit = total_letters_of_credit / 2
answer = average_letters_of_credit