I can't fully answer this question because it is incomplete. In order for me to help you, I could just define what a precipitation reaction is and give a concrete example.
A precipitation reaction consists of two aqueous solutions that when reacted together, forms an insoluble salt. For example,
AgNO₃ (aq) + HCl (aq) --> AgCl (s) + HNO₃ (aq)
In this case, the precipitate is AgCl, Silver Chloride, which appears as a white solid.
159.3 g
mol= mass (g)/ molecular weight (g/mol)
mass (m) = ? , volume = 18.0 ml , density = 1.42 g/ml .

I hope I helped you^_^