M(KOH)=56g/mol
M(NaOH)=40g/mol
V=250cm³=0,25dm³
m=12g
KOH:NaOH = 1:3
56 + 3*40 = 176g
176g -- 56g (KOH)
12g -- x g
x=3,8g - masa KOH
masa NaOH = 8,2g
masa H₂O = 250g
masa roztworu = 262g
Cp NaOH = 8,2 : 262 * 100% = 3,12%
Cp KOH = 3,8 : 262 * 100% = 1,45%