The 2008 income statement and balance sheet (excerpts) for BNSF Railway are below.

The 2008 income statement and balance sheet (excerpts) for BNSF Railway are below. BNSF Railway Company and Subsidiaries Consolidated Statements of IncomeYear ended Dec 31, (In millions)200820072006Revenues$17,787 $15,610 $14,816 Operating expenses:Fuel 4,640 3,327 2,856 Compensation and benefits 3,859 3,754 3,801 Purchased services 2,077 1,995 1,894 Depreciation and amortization 1,395 1,292 1,175 930 618 Operating income 3,896 3,510 3,542 113 (19) (191) (162)39 Income before income taxes 3,800 3,583 3,552 Income tax expense 1,438 1,384 1,314 Net income $ 2,362 $ 2,199 $ 2,238 BNSF Railway Company and Subsidiaries Consolidated Balance Sheets (excerpts)200724 Accounts receivable, net of allowance of $54 and $34873 805 Materials and supplies524 579 Current portion of deferred income taxes434 282 Other current assets337 325 Total current assets 2,377 2,015 Property and equipment, net30,838 29,560 Other assets 2,910 1,953 Total assets$36,125 $33,528 The footnotes included the following: Property & equipment, net (in millions) is as follows:Dec 31,200820071,751 $ 1,718 Track structure19,108 18,037 Other roadway12,922 12,370 Locomotives 4,210 4,003 Freight cars and other equipment 2,140 2,034 572Total cost 40,746 38,734 (9,174)Property and equipment, net $30,838$29,560Required:a. What proportion of total assets, does BNSF hold as property and equipment in 2008 and 2007? b. What economic assets might not be reflected on the BNSF balance sheet?c. By what percentage are the assets ‘used up’ at the year-end 2008?