A 0.5133g sample was dissolved and diluted to 1000mL in the determination of calcium in antacid tablets by atomic absorption. Three 5.00mL aliquots were diluted to 50.0mL each after addition of0, 1.0, and 2.0mL, respectively of a calcium standard containing0.500mg Ca/ mL. The absorbance of the three solutions was 0.310, 0.475, and 0.640. Calculate the mg Ca in the sample.