code for above diagram

> f:=piecewise(x<2.6050,.15*x, x<6.7200, .15*2.6050+.28*(x-2.6050),x<13.4930,.15*2.6050+
.28*(6.7200-2.6050)+ .33*(x-6.7200),100):

> p1:=plot(f,x=0..17):

> p2:=plot({[2.605,subs(x=2.605,f)],[6.7200,
subs(x=6.7200,f)]},style=point,thickness=3):

> plots[display]({p2,p1}, titlefont=[TIMES,BOLD,14],
title=`Tax vs Income in Tens of Thousands`,view=[0..17,0..3.5]);

>