Answer:
The answer to your question is 6 organisms.
Explanation:
Data
625 ft² -------- 1 multicellular organism
3750 ft² -- number of organisms
Process
1.- To know the number of organisms that can supply 3750 ft² of lawn, we need to use proportions and cross multiplication.
 625 ft² ------------------ 1 multicellular organisms
 3750 ft² ------------------ x
 x = (3750 x 1) / 625
 x = 3750 / 625
 x = 6
2.- Conclusion
3750 ft² can supply of oxygen 6 organisms.