One-half cup of black beans provides 15% of the potassium you need daily. you must get the remaining 2890 milligrams from other sources.

Not 100% sure on what you are asking but i think i got it. If you are looking for the amount of K (potassium) in milligrams then you need to first know that 85%=2890 milligrams. if you divide 2890 by 17 you get 5%=170 mg. multiply this by 3 to get 15%=510 mg. so one half cup of black beans has 510 milligrams of K. the total amount of K needed daily is 510+2890=3400 milligrams or 34 grams