A buffer solution with a pH of 12.00 consists of Na 3 PO 4 and Na 2

Question:

A buffer solution with a pH of 12.00 consists of Na₃PO₄ and Na₂HPO₄. The volume of solution is 200.0 mL.
(a) Which component of the buffer is present in a larger amount?
(b) If the concentration of Na₃PO₄ is 0.400 M, what mass of Na₂HPO₄ is present?
(c) Which component of the buffer must be added to change the pH to 12.25? What mass of that component is required?