Guesstimate rates from concentration ~ time plots

x = seq(0,2, by=1/100)
y1 = 0.7*x + 0.01
y2 = 0.2*x^2 + 0.01
y3 = 0.2*x^3 + 0.01
plot(y1 ~ x, type='l', ylab='relative concentration', xlab='time', lwd=2, ylim=c(0,1))
lines(y2 ~ x, col='red', lwd=2)
lines(y3 ~ x, col='blue',lwd=2)

dy1 = rep(0.7, length(x))
dy2 = 0.4*x
dy3 = 0.6*x^2
plot(dy1 ~ x, col='black', lwd=3, type='l', ylab='rate', xlab='time')
plot(dy2 ~ x, col='black', lwd=3, type='l', ylab='rate', xlab='time')
plot(dy3 ~ x, col='black', lwd=3, type='l', ylab='rate', xlab='time')