Helix Company purchased tool sharpening equipment in April 1, 2010 for $72,000. The equipment was expected to have a useful life of four years, or 9,000 operating hours, and a residual value of $2,700. The equipment was used for 2,400 hours during 2010, 4,000 hours in 2011, 2,000 hours in 2012, and 600 hours in 2013.

Instructions: Determine the amount of depreciation expense for the years ended December 31, 2010, 2011, 2012, and 2013 by each of the following methods:

1. Straight-line

2. The units of activity method

3. Double Declining balance method