pH of acid or base mixtures

Exercise 1

Determine the $pH$ of the solution obtained by mixing $V_1$ = 300 $mL$ $HCl$ 0.6 $M$ with $V_2$ = 200 $mL$ $HI$ 0.7 $M$

$HCl$ ,$ HI$ :    strong acids $n_{HCl}$ $=$ $c_{HCl}\cdot V_1$ = 0.18 $mol$ $n_{HI}$ $=$ $c_{HI}\cdot V_2$ = 0.14 $mol$ $pH$ $=$ $-log\frac{n_{HCl} + n_{HI}}{V_1+V_2}$ = 0.194