Washing soda has formula

Washing soda is:

Washing soda has the formula :

Washing soda has the formula :

Washing soda has the formula Na_(2) CO_(2).10H_(2)O . What is mass of anhydrous sodium carbonate left when all the water of crystallisation is expelled by heating 57.2 g of washing soda?

Washing soda has chemical formula……………… .