To determine the number of chickens that can be reared, first calculate the total floor area of the deep litter house by multiplying its dimensions: 9 m by 20 m, which equals 180 m². Next, divide the total area by the recommended floor space per chicken, 0.36 m², resulting in 500 chickens that can be accommodated in the house. This calculation ensures that each chicken has adequate space for movement and health.