What is the unit rate of 6 ounces of 2.5 servings?

Either divide both numbers by 6 or divide both numbers by 2.5 depending on how you want the answer to read, so

6/6 oz. for 2.5/6 servings or 1 oz. for. 41666 servings or

6/2.5 oz. = 2.5/2.5 servings or 2.4 oz. for 1 serving (this is the one you probably want)

6/6 oz for 2.5/6 serving or 1 oz for. 41666 serving