For A, the pH is 3.69 because you just solve it as a regular acid problem

For B, you just solve it as a regular base problem, ph= 11.66

For D, you solve it has a buffer solution of the second Ka2 acid rendering a ph of 10.33 (Am I right that this is a buffer solution AND you use the pH=pka+log([A-]/[HA])?)

For C, ph is 8.35 because of the plugging in formula.