CHEMISTRY: acid/base equilibrium

[applesnjanono]

Homework Statement

Calculate the end point pH when 50 mL 0.2 mol/L HCl solution reacts exactly with 50 mL 0.2 mol/L NH3 (equivalent to NH4OH) solution.

NH3 Kb=1.8x10^-5

The Attempt at a Solution

I have no idea how to even attempt this question. Can someone please help me? Thanks.

 

[Borek]

What is the composition of the solution at the end point? What ions are present? Only one them can change solution pH - which one?