$16\mathrm{.}80$ Using data from Appendix $D,$ calculate $O{H}^{-}$and $pH$ for each of the following solutions: $($a$)0\mathrm{.}105$MNaF, $($b$)0\mathrm{.}035MN{a}_{2}S,($c$)$ a mixture that is $0\mathrm{.}045M$ in $NaC{H}_2\frac{C}{O}O$ and $0\mathrm{.}055M$ in $Ba(C{H}_3\frac{C}{O}O{)}_2.$