Double-declining-balance rate:
By straight-line method, annual depreciation expenses = (85,000-5,000)/5 = $16,000
Rate of depreciation = 16000/(85,000-5,000) = 0.2 = 20%
Then, double-declining-balance rate = 2*Straight-line rate = 2*20 = 40%
From 2nd January 2017 to 31st December 2018 can be approximated as 1 year.
Therefore,
Depreciation expense in yr 1 = 40/100 * 85,000 = $34,000
And,
Book value at December 31 2018 = $85,000 - $34,000 = $51,000
It can be seen that the correct answer is b.
