A business property valued at $390,000 is depreciated over 39 years by the straight-line method, so its value x years after the depreciation began is...

A business property valued at ​$390,000 is depreciated over 39 years by the​ straight-line method, so its value x years after the depreciation began is V = 390,000 - 10,000x. Explain why the value of the property is a function of the number of years.