posted by peter .
a roller whose diameter is 20 in weight 72 lbs. what horizontal force is necessary to pull the roller
That will depend upon frictional torque on the roller axis. You have not provided enough information.
Is your word "weight" supposed to be the verb "weighs"? Does "in" mean inches?
I suspect you have omitted part of the question. Is the roller being pulled over a small bump, as in this question:
http://www.jiskha.com/display.cgi?id=1315698220 ? Such problems can be solved by balancing torques about the line of contact.