The Internet Economy
> c:=50+.8*y;
> In:=50;
> Gn:=120;
> Te:=c+In+Gn;
> Te:=y;
>
> plot({c,In,Gn,Te,age},y=0..1300,color=[black,black,black,black,black]);
> y:=-0.25*x^2-0.50*x +42;
> plot(y,x=0..12);
> y1:=-0.35*x^2-0.780*x +52;
> plot({y,y1},x=0..14);