The value of an automobile purchased in 2009 can be approximated by the function V (t) = 25(0.85)t, where t is the time, in years, from the date of purchase, and V (t) is the value, in thousands of dollars.

(a) Evaluate and interpret V (4), including units.

(b) Find an expression for V'(t), including units.

(c) Evaluate and interpret V'(4), including units.

(d) Use V (t), V'(t), and any other considerations you think are relevant to write a paragraph in support of or in opposition to the following statement: "From a monetary point of view, it is best to keep this vehicle as long as possible."