9. Property, plant and equipment December 31, Useful Lives (Years) $ 20-45 2-10 (Millions of dollars) Land Buildings and land improvements Machinery, equipment and other Software. Equipment leased to others Construction-in-process Total property, plant and equipment, at cost. Less: Accumulated depreciation... Property, plant and equipment-net 2018 6715 6,977 13,733 1,703 6,015 682 29,781 (16,207) 13,574 $ 2017 664 7.515 14,888 1.745 6,038 688 31.538 (17,383) 14.155 $ a. Calculate the percent-used-up of Caterpillar's fixed assets. b. Calculate average useful life of the company's fixed assets. 9. Property, plant and equipment December 31, Useful Lives (Years) $ 20-45 2-10 (Millions of dollars) Land Buildings and land improvements Machinery, equipment and other Software. Equipment leased to others Construction-in-process Total property, plant and equipment, at cost. Less: Accumulated depreciation... Property, plant and equipment-net 2018 6715 6,977 13,733 1,703 6,015 682 29,781 (16,207) 13,574 $ 2017 664 7.515 14,888 1.745 6,038 688 31.538 (17,383) 14.155 $ a. Calculate the percent-used-up of Caterpillar's fixed assets. b. Calculate average useful life of the company's fixed assets