par(mfrow=c(2,1))
plot(ibm[,1], xlim=c(1954,2000), ylim=c(0,200),
ylab="Sales (billions of $)", xlab="Year", type="o")
lines(ibm[,3],col=2,type="o")
plot(ibm[,2], xlim=c(1954,2000), ylim=c(-10,30),
ylab="Profits (billions of $)", xlab="Year", type="o")
lines(ibm[,4],col=2,type="o")
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