For the titration of $25\mathrm{.}00mL$ of $0\mathrm{.}081$mOl$/$L benzoic acid $)=(6\mathrm{.}410-5$ with $0\mathrm{.}100$mol$/$L of sodium hydroxide, NaOH, calculate the $pH$

a$)$ before adding any NaOH $($aq$).(2$ marks$)$

b$)$ after $10mL$ of NaOH$(aq)$ has been added $(4$ marks$)$

c$)$ At the equivalence point $(4$ marks$)$