Able Towing Company purchased a tow truck for $180,000 on January 1, 2016. It was originally depreciated on a straight-line basis over 10 years with an assumed salvage value of $36,000. On December 31, 2018, before adjusting entries had been made, the company decided to change the remaining estimated life to 4 years (including 2018) and the salvage value to $5,000. What was the depreciation expense for 2018