问答题 考虑一下由以下方程式所描述的经济：
   Y=C+I+G+NX
   Y=5000
   G=1000
   T=1000
   C=250+0.75(Y-T)
   I=1000-50r
   NX=500-500ε
   r=r^*=5
   a．在这个经济中，求出国民储蓄、投资、贸易余额以及均衡汇率。
   b．现在G增加到1250，求出国民储蓄、投资、贸易余额以及均衡汇率的值。解释你的结果。
   c．现在假设世界利率从5/%上升到10/%(G又是1000)，求出国民储蓄、投资、贸易余额以及均衡汇率的值。解释你的结果。
   Consider an economy described by the following equations：
   Y=C+I+G+NX
   y=5000
   G=1000
   T=1000
   C=250+0.75(Y-T)
   I=1000-50r
   NX=500-500ε
   r=r^*=5
   a．In this economy, solve for national saving, investment, the trade balance, and the equilibrium exchange rate.
   b．Suppose now that G rises to 1,250. Solve for national saving, investment, the trade balance, and the equilibrium exchange rate. Explain what you find.
   c．Now suppose that the world interest rate rises from 5 to 10 percent. (G is again 1,000). Solve for national saving, investment, the trade balance, and the equilibrium exchange rate. Explain what you find.