4. MT&A uses the function () 475 - 15x, to depreciate smart phones, where / represents the value of a smart phone and x represents the number of months since its purchase. Part A: Find and explain what it represents in this situation. Part B: When will the depreciated value of a smart phone be less than $1002 Part C: What does x represent in f-1(x) = 30° What is the value of x? Part D: Graph f(x) and f-(x) on the same coordinate plane below. MATH NATION Camion​