Assume that supply for replacement mobile phone batteries in the Australian domestic market is given by the inverse-supply expression P = 9+0.00001QS , while inverse demand is P = 19 0.00001QD. The world price for batteries is $10. (a) (4 marks) Find the equilibrium price and quantity in the market for replacement mo- bile phone batteries if Australia does not engage in any international trade. Compute the consumer surplus, the producer surplus, and the total surplus in the market. (b) (7 marks) Now assume that Australia trades on the world market for batteries, exporting or importing batteries depending on the relation between the world and domestic prices. Find the price at which batteries will be sold in Australia, the quantity purchased, the quantity produced, and the quantity of imports or exports. Compute the consumer surplus, the producer surplus, and the total surplus in the market, as well as the gains from trade relative to part (a).