what is the percent by mass concentration of a solution that contains 5.30 grams of salt dissolved in 19.7 g of water

The pressure in a fluid is affected by which characteristics of that fluid

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?

Can someone me with 3 and 4 plz. this is for masteries test.