Postal Restrictions

The U.S. Postal Service will only mail packages that meet certain size requirements. For cylinder-shaped packages (or “rolls”), the minimum length is 4 inches and the maximum length is 36 inches. There is also a restriction that the length plus two diameters can be no more than 42 inches (why do you think they have this restriction?).

What are the dimensions of an acceptable cylinder-shaped package that will have the greatest volume?