Use the 45-degree line for an open economy (DD and ZZ curves) to analyze the effect of a real depreciation. Draw the DD and ZZ curves so that the equilibrium before the change means that the trade balance (NX) is zero. Assume that the Marshall-Lerner condition is met so that depreciation increases net exports, all other things being equal. Show which curve(s) are shifted and where the new equilibrium for Y arises