A solution of 12.50 mM of compound X and 11.75 mM of compound Y gave peak areas of 7.55 and 7.02 cm2 on a chromatogram. A solution containing an unknown amount of X and 10.25 mM of Y was run and gave peak areas of 8.20 and 6.50 cm2 respectively. What is the concentration of X in the unknown solution? What kind of standard is Y?