Question 18 (3 points) Consider the demand equation for cigarettes In Q = a + 3In P + u where Q. P, and u denote the quantity, price and unobserved error term respectively. The general tax per pack in a given state can be a valid instrument for InP because of the following reasons except changes in the tax affects profitability of cigarette producers. changes in the tax does not affect the demand of cigarettes at all. changes in the tax does not shift the demand curve. changes in the tax shifts the supply curve