data=read.table("gasdata.txt",header=TRUE)
attach(data)

Y=gal
X1=Tax
X2=Inc
X3=high
X4=drvlic

LM=lm(Y~X1+X2+X3+X4)
summary(LM)

RM1=lm(Y~X1+X2+X4)
summary(RM1)

anova(RM1,LM)
drop1(LM)

step(LM,direction="backward")