(8 pts) Let us consider again the basic andy model with the added advert quadratic term. sales = ,6'1 + 62mice + Bgddvert + madam-1&2 + e (3) i. The partial (or marginal) effect of a regressor ink on the response y is determined by the partial derivative 2"? Please derive the marginal effect of advert. 63k ii. If the advert is equal to average level of data, please calculate the marginal effect of advert using data