Explain how a tariff reduction causes an increase in the equilibrium quantity of imports and a decrease in the equilibrium price. Hint: Consider the Work It Out "Effects of Trade Barriers."
This is the opposite case of the Work It Out feature. A reduced tariff is like a decrease in the cost of production, which is shown by a downward (or rightward) shift in the supply curve.
Explain how a subsidy on agricultural goods like sugar adversely affects the income of foreign producers of imported sugar.
A subsidy is like a reduction in cost. This shifts the supply curve down (or to the right), driving the price of sugar down. If the subsidy is large enough, the price of sugar can fall below the cost of production faced by foreign producers, which means they will lose money on any sugar they produce and sell.