Knife Edge Company purchased tool sharpening equipment on July 1, 2010, for $16,200. The equipment was expected to have a useful life of three years and a residual value of $900.

Determine the amount of depreciation expense for the years ended December 31, 2010, 2011, 2012, and 2013, by (a) the straight-line method and (b) the double-declining-balance method.

I want to know how to come to each conclusion. The book makes no sense in explaining each of these methods. Thanks!