For a solution that is 0.275 M CH₃CH₂COOH (propionic acid, Kₐ=1.3×10⁻⁵ and 0.0892 M HI, calculate:
(a) H₃O⁺
(b) OH⁻
(c) CH₃CH₂COO⁻
(d) I⁻