$pH$ of a mixture weak acid $HB$ / corresponding base $B$ (Buffer)

Established by the strict method

$v_{HB}\;=$ $mL$ $c_{HB}\;=$ $\frac{mol}{L}$ $v_{B}\;=$   $mL$ $c_{B}\;=$    $\frac{mol}{L}$ $pK_a\;=$

$pH$ = ........