x=structure(list(Vt = c(0, 0.34, 3.68, 10.38, 21.94, 32.08, 48.54, 79.69, 94.82, 107.99), t = c(0L, 3L, 6L, 9L, 12L, 16L, 24L, 36L, 48L, 72L)), .Names = c("Vt", "t"), class = "data.frame", row.names = c(NA, -10L))
m4=nls(Vt~(107.99)/(1+exp(2-4*k*(t-g))), data=x, start=c(k=0.05,g=0.1))
m4
f4=function(x){(107.99)/(1+exp(2-4*0.02853*(x-8.71643)))}
curve(f4, 1,100)