What mass of Pb(No3)2 would be required to yield 9g of 3PbCl2 on the addition of excess sodium chloride solution

I have no idea what you mean by 3PbCl2. I will assume that is PbCl2.

PbCl2 + 2NaCl ==> PbCl2 + 2NaCl
Using the coefficients in the balanced equation, convert mols PbCl2 to mols Pb(NO3)2.
Now convert mols Pb(NO3)2 to grams. g = mols x molar mass = ?
mols Pb(NO3)2 = grams/molar mass = ?