2NaOH+ H2SO4---->Na2SO4+2H2O
md NaOH= ms*c/100= 84 kg
din ecuatia reactiei:
2*40kg NaOH........98kg H2SO4.......142 kg
84 kg.............................x.....................y
x=....... reprezinta md H2SO4 si din formula c%=md*100/ms ==>ms H2SO4
y=........kg Na2SO4