A `2.0 g` of mixture of `Na_(2)CO_(3)` and `NaHCO_(3)` loses `0.248 g` when heated to `300^(@)C`, the temperature at which `NaHCO_(3)` decomposes to `Na_(2)CO_(3)`, `CO_(2)`, the temperature at which `NaHCO_(3)` decomposes to `Na_(2) CO_(3), CO_(3)` and `H_(2) O`. What is the percentage of `Na_(2) CO_(3)` in mixture?