HNO₂ (aq) + NH₃ (aq) ⇄ NH₄⁺ (aq) + NO₂⁻ (aq)

Nitrous acid reacts with ammonia according to the balanced chemical equation shown above. If 50 mL of 0.20 M HNO₂ (aq) and 50 mL of 0.20 M NH₃ (aq) are mixed and allowed to reach equilibrium at 25°C, what is the approximate [NH₄⁺] equilibrium?
a. 0.00010 M
b. 0.0010 M
c. 0.010 M
d. 0.10 M