to solve this problem, you need to know the total mass of the type of food you're considering. For example, if the total mass is 100g, then the percentage of sodium is .
Now, if you need a daily percent, you need to know the quantity of food per day together with the quantity of sodium per day and then apply the same idea as above. This should give you the same answer since we're assuming that if per day you eat 10% of the total mass of the food, then you'll be eating also 10% of the total mass of sodium.
hope this helps,