A model for advertising response is given by N(a) = 6000 + 400 In a where N(a) is the number of units sold and a is the amount spent on advertising in thousands of dollars. a) Interpret the meaning of N(3) &~ 6439 in context of the problem. Use complete sentences. x b) Find N'(2), then interpret the meaning of N'(2) in context of the problem. Use complete sentences