y.low <-               # you fill this in and adjust as needed
                       # to create a plot in which the horizontal
                       # and vertical limits frame the curves
                       # to be plotted without cutting them off
                       # and without a lot of extraneous space
                       # in which the curve isn't interesting;
                       # i suggest starting with y.low = 0

y.high <-              # you fill this in and adjust as needed;
                       # i suggest starting with y.high = 4

y.grid <- seq( y.low, y.high, length = 500 )

max.density <-         # you fill this in and adjust as needed;
                       # i suggest starting with max.density = 1

plot( y.grid, dweibull( y.grid, 1, 1 ), xlab = 'y', ylab = 'Density',
  type = 'l', lwd = 2, ylim = c( 0, max.density ) )

lines( y.grid, dweibull( y.grid, 2, 1 ), lwd = 2, lty = 2, col = 'red' )

lines( y.grid, dweibull( y.grid, 4, 1 ), lwd = 2, lty = 3, col = 'blue' )

# and so on