here NH4HS is solid so pressure contributed by NH3 and H2S calculate Kp ,then again derive equation in the presence of NH3 with some partial pressure,KP =p(p +NH3 partial pressure),Kp remains constant at same temprature.consult p bahadur many numericals r there in chemical eq.
Arun / Rashi - Authors Macromind MCQ of Chemistry from G.R Batla