Indium is seldom found in lead-containing samples and thus makes a good internal standard for lead analyses. A 10.0 mL aliquot of a 1.00x10-4 M Pb(II) solution is added to 10.0 mL of a 1.00x10-4 M solution of In(III). The resulting currents, measured polarographically, are 0.485 and 0.873 mA for Pb(II) and In(III), respectively. Then, 2.00 mL of a 2.00x10-4 M In(III) solution are added to 10.0 mL of a sample and the currents for Pb(II) and In(III) are 0.186 and 0.504 mA, respectively. Assuming a linear response between current and concentration, calculate the concentration of Pb(II) in the sample by (a) neglecting the information provided by the internal standard, and

(b) taking the internal standard into account the correct answer is (a) 2.30x10-5 M, (b) 2.66x10-5 M <-- how to get these answer?