$2$

$[15]$ If an asset has an initial cost of $$120,000$ with a $$20,000$ salvage value after eight $(8)$ years, compute the depreciation schedule using:

a$)$ Straight$-$line method

b$)$ Sum of Year's Digit method

c$)$ Double declining method

Also, plot the book value over the service life of the three methods on the same graph.