IS: Y=C+I+G=400+0.8Y+350-100i+250 =1,000+0.8Y-100i=> 0.2Y=1,000-100i ...(1)
LM: L=800+0.4Y-100i=3,200/2=Ms/P=> 0.4Y-100i=800 ...(2)
(1)+(2) => 0.6Y=1,800 故Y=3,000
再將Y代回IS或LM,即可得i=4