-calculez masa de NaOH din solutie
c= mdx100/ms; 20/100=md/400-----> md=80gNaOH
-din ecuatie, calculez masa de acid ce reactioneaza cu masa de baza obtinuta
60g................40g
CH3COOH+ NaOH---> CH3COONa+H2O
x=120.............80
-calculez masa de solutie de acid ce contine md= 120g acid
30/100= 120/ms........................calculeaza ms!