What Is the Concentration of Ammonium Ion in a 0 $\times$

What is the concentration of ammonium ion in a 0.150 M solution of ammonia? The K_b value for ammonia is 1.80 $\times$ 10^-5.

A) 0.146 M
B) 0.148 M
C) 2.34 $\times$ 10^-5 M
D) 1.63 $\times$ 10^-3 M
E) 4.20 $\times$ 10^-3 M