Please help- I am unsure of which signal equation to use and what to plug in for which variables?

Answer all questions in the spaces provided. 1. A 20.0-mL aliquot of an aqueous quinine solution was diluted to 100.0mL and the absorbance was measured at 348nm in a 1.00cm cell. A second 20.0mL aliquot of quinine solution was mixed with 10.0mL of 25.0ppm quinine and then diluted to a final volume of 100.0mL and its absorbance measured in a 1.00cm. cell. If the absorbance of the first solution was 0.398 and the absorbance of the second solution was 0.505, calculate the concentration of quinine in the original aqueous solution