How many grams of sodium flouride should be added to 100000 litres of drinking water containing 0.6ppm of sodium flouride to provide a recommendation concentration of 1.75ppm?

Answer 1

If you use x kg of NaF, then assuming that the water weighs 1kg/L,
x + .06/10^6 * 10^5 = 1.75/10^6 (x + 10^5)