On January 1, Year 1, Ballard company purchased a machine for $64,000. On January 1, Year 2, the company spent $25,000 to improve its quality. The machine had a $17,200 salvage value and a 6-year life, which are unchanged. Ballard uses the straight-line method. What is the book value of the machine on December 31, Year 4?

a) $37,800

b) $42,800

c) $12,800

d) $25,600