The following property and equipment section was obtained from a recent Abbott Laboratories 10-K. Property and equipment, at cost Land... Buildings... $ 370,949 2,655,356 Equipment... Construction in progress.. Less: accumulated depreciation and amortization............ Net property and equipment..... 8,813,517 920,599 12,760,421 6,757,280 $ 6,003,141 Property and Equipment Depreciation and amortization are provided on a straight-line basis over the estimated useful lives of the assets. The following table shows estimated useful lives of property and equipment. Classification Buildings.... Equipment.... Estimated Useful Lives 10 to 50 years (average 27 years) 3 to 20 years (average 11 years) During the year, the company reported $868,808 for depreciation expense. What is Abbott Laboratories' estimated useful life of depreciable assets?