help please. Stuck at this question.....Can do this with Ka given...?

Question

A solution is prepared by adding 57.0 mL of 0.050 M HCl to 143.0 mL of 0.30 M HNO3. Calculate the concentrations of all species in this solution.
[H+]

[OH -]

[Cl -]

[NO3-]

Answer 1

Since these acids are "strong", you don't use Ka; all ions are considered dissolved. So you calculate each from
Conc(mole/liter) = SUM (volumexmolarity)/SUM(volume)

Once you have H+, [OH-] = 10-14/[H+]