1 pts A small country is facing the following domestic supply curve of a product: S = 200 + 20P, as well as the following domestic demand curve of a product: D = 400 - 20P. It can import it at a world price of 10 per unit. In addition, each unit of production yields a marginal social benefit of 10. The effect on welfare of an import tariff of 6 per unit is $ 320 O -480 -320 420 O -500 O -420 180 O 500 O -180 Oo