Consider three small countries - Country A, Country B, and Country C - producing and consuming one good - Good X.

Country A is the domestic (home) country producing and importing Good X. Country B produces Good X at $6. Country C produces Good X at $5.

In Country A, the linear downward sloping demand curve for Good X starts at Quantity = 0 when Price = $15. The linear upward sloping domestic supply curve for Good X starts at Q = 0 when P = $3.

Initially, Country A imposes a flat tariff of $2 on the import of Good X. Country A produces 9 units of Good X domestically, and imports 6 units of Good X.

a) Suppose Country A and Country C form a customs union. Analyse the changes and implications using a diagram. (Note: For this question, there is no need to calculate the sizes of the welfare areas mathematically, i.e., there is no need to derive the value of consumer surplus, etc.)