Following are selected disclosures from the 10-K report of Facebook Inc. Property and Equipment, Net

$ millions	2015	2014
Land	$596	$153
Buildings	2,273	1,420
Leasehold equipment	447	304
Network equipment	3,633	3,020
Computer software, office equipment and other	248	149
Construction in progress	622	738
Total	7,819	5,784
Less: Accumulated depreciation	(2,132)	(1,817)
Property and equipment, net	$5,687	$3,967

Depreciation expense on property and equipment was $1.22 billion, $923 million, and $857 million during 2015, 2014 and 2013, respectively.

(a) Compute the PPE turnover for 2015 (Sales in 2015 are $17,928 million) => PPE turnover is 3.71

(b) Estimate the useful life, on average, for its depreciable PPE assets. (Years)

Round your answer to two decimal places.

(c) By what percentage are Facebook's assets "used up" at year-end 2015?

Round your answer to two decimal places.