fe+2hcl>fecl2+h2
x/56=5.6/22.4
x=14 m(cu)=20-14=6
14/20=0.7*100=70%
6/20=0.3*100=30%
амега (Nа2SО4) = m (Nа2SО4)/m (раствора) = 50/250 = 0,2*100\% = 20\%