Here is a $0.400\;M$ solution of $HN_3$
(hydrazoic acid, $K_a = 1.9\cdot 10^{-5}$)
Equilibrium of hydrolysis:
$HN_3$ $+$ $H_2O$ 
$H_3O^+$ $+$ $N_3^-$
Identify please the initial concentrations (without $H_2O$):
a) $0\;M$, $0.400\;M$, $0\;M$ b) $0.400\;M$, $0.400\;M$, $0.400\;M$ c) $0\;M$, $0\;M$, $0.400\;M$ d) $0.400\;M$, $0\;M$, $0\;M$
Initial concentrations: d) $0.400\;M$, $0\;M$, $0\;M$