A business purchasing an item for business purposes may use straight-line depreciation to obtain a tax deduction. The formula for the present value, \(P\), after \(t\) years is

\[P=C-\left(\frac{C-s}{L}ight) t\]

where \(C\) is the cost and \(s\) is the scrap value after \(L\) years. The number \(L\) is called the useful life of the item.

a. If a certain piece of equipment costs \(\$ 20,000\) and has a scrap value of \(\$ 2,000\) after 8 years, write an equation to represent the present value after \(t\) years.

b. Graph the amount you will have in \(t\) years.

c. What is the slope of the graph?