2NaHCO3 = NaCO3 + CO2 + H2O
..2*84.(44+18)
.x.(27.4-21.2)
x = 16.8(g)
w(NaHCO3)= 16.8/27.4 =61.3%
w(Na2CO3)= 1-61.3% = 38.7%