data.source<-"http://www.math.mcgill.ca/dstephens/Regression/Data/2-1-RocketProp.csv"

RocketProp<-read.csv(file=data.source)

names(RocketProp)<-c('i','Strength','Age')

x<-RocketProp$Age
y<-RocketProp$Strength
plot(x,y)

plot(x,y,pch=19)

plot(x,y,pch=19,xlab='Age',ylab='Shear Strength')

(xmean<-mean(x))
(ymean<-mean(y))

abline(v=xmean,h=ymean,lty=2)