$pH$ of a mixture strong acid $HB_1$/ strong base $B_2$

Established by the strict method

$v_{HB_1}\;=$ $mL$ $c_{HB_1}\;=$ $\frac{mol}{L}$ $v_{B_2}\;=$   $mL$ $c_{B_2}\;=$   $\frac{mol}{L}$

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