Equipment was acquired on January 1, 2013, at a cost of Php75,000. The equipment was originally estimated to have a salvage value of Php5,000 and an estimated life of 10 years. Depreciation has been recorded through December 31, 2016, using the straight-line method. On January 1, 2017, the estimated salvage value was revised to Php7,000 and the useful life was revised to a total of 8 years.

1. Calculate the book value at the time of the revision (January 1, 2017).
2. Determine the depreciation expense for 2017