If Country A produces 600 corn it will use 1.5 acres of land. The total land used is only 3.5 acres, a saving of 3 acres over the non-trade regime. This shows that there are gains from trade. In this example, resources are freed in Country B, they can be used to produce goods, a portion of which Country B will willingly give to Country A if Country A agrees to this deal. There are two types of trade restrictions that are commonly applied to international trade.
Tariffs are a tax on imports.
Quotas limit imports to a certain quantity. Both increase the price of imported goods. The remainder will be supplied from abroad. Shift the international supply curve up and you will see that imports fall, American consumers buy less, but American producers produce more. At any lower price there will be a shortage of cars, as only 100,000 are permitted to be imported.