Here's how I would handle it. First off, you're given the masses in mg of the sodium and the potassium present in 0.25 tsp. Then they give you the mass of 1.0 tsp in grams (6.0 grams). So I'd convert the mg into grams. This will give you 0.290 grams of Na and 0.340 grams of potassium. Those masses will be present in 6.0/4= 1.5 grams of salt. Now, you need to find the number of moles of sodium and potassium you have present since each mole of sodium and each mole of potassium have one mole of chlorine. So for sodium you would find the number of moles you have, then multiply by the molar mass of chlorine to get the number of moles of chlorine from the NaCl. Then you would do the same for the potassium. Now for each of the salts just add together the mass of the metal and the chlorine, and divide by the mass of 0.25 tsp of salt (1.5 grams). Multiply by 100 and there is your percentage for each of them. You will find that the % will NOT equal 100% because Iodide ions are added to salt in very small amounts. Does that make sense?