17) The function v=f(t) gives the median value of a home (in thousands of dollars) in the metro phoenix area as a function of time in years since 1990. What are the units on f '(t) ?

a)Thousands of dollars

b)Dollars per year

c)Thousands of dollars per year

d)Thousands of dollars per home

e)None of these

I have no clue, I dont get the topic of derivatives at all. Any help would be appreciated.