pH of acid or base mixtures

Exercise 1

Determine the $pH$ of the solution obtained by mixing $V_1$ = 500 $mL$ $HBr$ 0.05 $M$ with $V_2$ = 350 $mL$ $HCl$ 0.65 $M$

$HBr$ ,$ HCl$ :    strong acids $n_{HBr}$ $=$ $c_{HBr}\cdot V_1$ = 0.025 $mol$ $n_{HCl}$ $=$ $c_{HCl}\cdot V_2$ = 0.2275 $mol$ $pH$ $=$ $-log\frac{n_{HBr} + n_{HCl}}{V_1+V_2}$ = 0.527