What is pH buffer of 0.1 mol L-1 Na2HPO4/O.15 mol L-1 KH2PO4?

Question

KH2PO4?
Given Ka(H2PO4-) = 6.2 x 10-8).

I would like to know the correct formula, steps for the answer

Thank you

Answer 1

pH = pKa + log [(base)/(acid)]
pH = 7.2 + log (0.1/0.15)
[H = 7.02.
Check my work.