There are 19.5 g Na in 71.4 g NaHCO₃ 
Calculate the molecular mass of NaHCO₃. 
1 Na = 1 × 22.99 u = 22.99 u 
1 H = 1 × 1.008 u = 1.008 u 
1 C = 1 × 12.01 u = 12.01 u 
3 O = 3 × 16.00 u = 48.00 u 
 TOTAL = 84.008 u 
So, there are 22.99 g of Na in 84.008 g NaHCO₃. 
∴ Mass of Na = 71.4 g NaHCO₃ × (22.99 g Na/84.008 g NaHCO₃) = 19.5 g Na