The value of an automobile purchased in 2007 can be aproximated 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)

b.) Find an expression for the derivative of V(t), including units.

c.) Evaluate and interpret V'(4)

d.) Use V(t) and 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."

I really want to see feedbacks for question d, so please explain it in details. Thank you!