In 2016, Donald Trump won the US presidential promising to renegotiate PTAs such as the North American Free Trade Agreement (NAFTA) to increase tariffs. In this exercise, we will analyse the impact of those threats on Mexican beer producers. We will assume this market is monopolistic competitive and products are differentiated (i.e. consumers cannot perfectly substitute across beers). Let's assume there are four Mexican firms producing different beers deciding whether to export to the US in 2017. These four firms have the following marginal costs: c1 = 1, c2 = 2, c3 = 3, and c4 = 4. Beer could be exported duty-free to the US under NAFTA. Each firm i faces the following demand in the US: Qi = 10 pi where pi is the price firm i charges for its beer variety. To enter the US market, firms have to pay a per-year entry cost of F = 10 to be able to sell in the US before knowing what trade policy will be in place. 1. Derive the optimal price and quantities for each Mexican firm in the US market under NAFTA assuming tariffs will not increase for sure