"Parts per million" sounds so teeny-tiny, whereas "milligrams per kilogram" sounds pretty substantial. Yet they are the same.
To convert to pounds, take your 2.75mg/kg and divide by 2.2 (2.2 pounds are in a kilogram) to get 1.25mg per pound.
The other one you have to do yourself or Ghazzu will accuse me of being a know-it-all gunner (which I was, in school, LOL) but it's going to obviously be a lot less per pound, right? By feeding 4 pounds you're going to get close to what a pound of the other stuff will get you, but not quite as much.
If you can keep "milligrams per kilogram" in your head and roughly divide by two, you can easily get a rough estimate of "milligrams per pound" if that is the unit of measure you are used to using. However, keeping units of measure in the same scale (metric) is pretty standard.