Gulf Consulting Col reported the following in its December 31, 2011, balance sheet: Equipment (at cost) $700,000. In a disclosure note, Gulf indicateds that is uses straight-line depreciation over five years and estimates salvage value as 10% of cost. Gulf's equipment averages 3.5 years at December 31, 2011. What is the book value of Gulf's equipment ad December 31, 2011?

a. $210,000, b. $259,000, c. $490,000, d. $441,000