What is the pH of a solution that contains 0.045 moles of NH4+ and 0.0090 moles of NH3? The pKa of ammonia is 9.25. Need help with process..?

NH₄⁺(aq) + H₂O(l) ⇌ NH₃(aq) + OH⁻(aq) .... pKₐ = 9.25

Let V L be the volume of the solution.
[NH₄⁺] = 0.045/V M
[NH₃] = 0.0090/V M
Then, [NH₄⁺]/[NH₃] = 0.045/0.0090

pH = pKₐ - log([NH₄⁺]/[NH₃])
pH = 9.25 - log(0.045/0.009)
pH = 8.55