Answer:
240 kilograms
Step-by-step explanation:
The productivity is the rate at which energy is added to the bodies of organisms in the form of biomass (amount of matter in the body).
The total biomass in the body of a heterotroph = 1560 kilograms
Biomass used in the respiration = 900 kilograms
Egested matter = 420 kilograms
Net secondary production = 1560 - 900 - 420
Net secondary production = 240 kilograms