Х г                                                                                  209,5 г

   Na3PO4         +          3AgNO3     =     3NaNO3      +     Ag3PO4

n = 1 моль                                                                        n = 1 моль

Mr = 164 г/моль                                                               Mr = 419 г/моль

m = 164 г                                                                          m = 419 г

Х г Na3PO4      -      209,5 г Ag3PO4

164 г Na3PO4   -     419 г Ag3PO4

m(Na3PO4) = 164 * 209,5 / 419 = 82 г