When reading the question ... You should automatically underline the key bits of information. This includes what each of the units are (g) solid mass, (cm3) volume , (moldm3) concentration. This will give you a huge hint as to what FORMULA you will have to use....
Mass : n=m/M
Number of molesis equal to the mass which is given in the question divided by the molar mass which may be in question if not you must work it out using the periodic table