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In case you need to plot distributions using R, the following code should do the trick.
plot(function(x) dnorm(x, 30, 15), -20, 80, ylab="Density", xlab="Size", col="dark green", lwd=2)
if for some reason you need to change the scale of the x axis:
plot(function(x) dnorm(x, 30, 15), -20, 80, ylab="Density", xlab="Size", col="dark green", lwd=2, xaxt="n")
axis(side=1, at=seq(-20,80,20), labels=(seq(-20,80,20)))
the sequences used for at and labels need to be of the same lenght.