person1<-function(x) { x }
person2<-function(x) { 2 * (x-10)}
plot(0, type="n", xlim=c(0,50), ylim=c(0,100), xlab="t", ylab="Performance")
curve(person1, 0, 50, add=T, col="blue")
curve(person2, 10, 50, add=T, col="red")
legend("topright", legend=c("Person with 1H", "Person with 2H"), pch=c(4,4), col=c("blue", "red"))

person1<-function(x) { 1 * exp(0.15 * x) - 1 }
person2<-function(x) { 4 * exp(0.15 * (x - 10)) -  4}
plot(0, type="n", xlim=c(0,50), ylim=c(0,500), xlab="t", ylab="Performance")
curve(person1, 0, 50, add=T, col="blue")
curve(person2, 10, 50, add=T, col="red")
legend("topright", legend=c("Person with 1H", "Person with 4H"), pch=c(4,4), col=c("blue", "red"))