I do not understand

4. Effects of a tariff on international trade The following graph shows the domestic demand for and supply of maize in Bolivia. The world price (Pw ) of maize is $240 per ton and is displayed as a horizontal black line. Throughout the question, assume that all countries under consideration are small, that is, the amount demanded by any one country does not affect the world price of maize and that there are no transportation or transaction costs associated with international trade in maize. Also, assume that domestic suppliers will satisfy domestic demand as much as possible before any exporting or importing takes place. ? 480 Domestic Demand Domestic Supply 420 390 360 330 PRICE (Dollars per ton) 300 270 240 210 180 30 60 90 120 150 180 210 240 270 300 QUANTITY (Tons of maize) If Bolivia is open to international trade in maize without any restrictions, it will import tons of maize. Suppose the Bolivian government wants to reduce imports to exactly 60 tons of maize to help domestic producers. A tariff of $ per ton will achieve this. A tariff set at this level would raise $ in revenue for the Bolivian government