a roller whose diameter is 20 in weight 72 lbs. what horizontal force is necessary to pull the roller

Answer 1

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.