The demand for shes in a country is given by D=60-0.5P, where P is the price of a pair of shoes. Supply by domestic producers is given by S=20+0.5P. The world price of a pair of shoes equal 30. In equilibrium, when this economy is closed to trade, the quantity of shoes demanded domestically equals ___, and when this economy opens to trade, the quantity of shoes demanded domestically equlas ___. How should I calculate this?

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