4. [10 Points] The salvage value S (in dollars) of a company jet after t years is estimated to be given by the formula below. S(t) = 300,000 (0.8)t Use the model to answer the following questions and interpret your results. (a) What is the rate of depreciation (in dollars per year) after 1 year? (b) What is the rate of depreciation (in dollars per year) after 5 years? (c) What is the rate of depreciation (in dollars per year) after 10 years