What is the pH of a solution with a [H_3O^+] of 3.45*10^-6 M?

$p H$ of the solution is $5.46$.
pH of a solution is=$- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$
=-log_10(3.45×10^-6)=5.46(ans).