Based on past experiences, the department store is aware that high price fluctuations$/$discounts may train the customers to become strategic so that they deliberately delay their purchase to potentially enjoy a discount. In view of this, the store manager has decided that the price in month $2$ cannot be less than $90\%$ of the price in month $1,$ and the price in month $3$ cannot be less than $80\%$ of the price in month $2.$ With the above additional requirements, how would you decide the optimal pricing policy? There is no need to use the excel solver to solve for the optimal prices; it is enough to just develop the model formulation.