Convert 76.8 cm to m.

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?

Is this correct if not can u correct me

What is the approximate mass of 25 cm3 of silver, if the density is 10.5 g/cm3? a. 0.42 g b. 2.4 g c. 42 g d. 260 g