A monoprotic acid with a Ka of 2.92 × 10-5 has a partition coefficient of 4.2 (favoring octanol) when distributed between water and octanol. Find the formal concentration of the acid in each phase when 100 mL of 0.10 M aqueous acid is extracted with 31 mL of octanol at (a) pH 4.00 and (b) pH 8.00.