A white powder, consisting of a simple mixture of tartaric acid (C4H6O6) and citric acid (C6H8O7) was analysed to determine the elemental composition. Combustion of a 429.6-mg sample produced 526.3 mg of CO2 and 156.4 mg of H2O. Use atomic masses: C 12.011; H 1.00794; O 15.9994. Calculate the percent carbon, by mass, in the sample.