Development Time Constants

This question is within the context of the subject title.

ALL things being equal, if HP5+ is given X minutes to
develop, what is the value of the constant K in the equation
X times K equals Y. Y is the time needed to develop Delta 3200.

I think the value of K may hold steady for all films in the same
developer. If so, some film, Plus X perhaps, may be used to
establish base times and a constant K applied to each
of any other films in that same developer.

To the point, I've from the woods ONE roll of Delta 3200 to
develop. If ten minutes will do for a roll of HP5+ how many
minutes should I give the Delta? Or, by what factor should
I multiply the ten minutes? Dan