Answer: There are 16 fish that he can keep in the aquarium.
Step-by-step explanation:
Since we have given that 
Length of aquarium = 4 feet
Width of aquarium = 1 foot
So, it forms a shape of cuboid.
As we know the formula for "Volume of Cuboid":

According to question, Each fish needs atleast 0.5 cubic feet of water.
So, Number of fish that he can keep in the aquarium is given by

Hence, there are 16 fish that he can keep in the aquarium.
 
        
             
        
        
        
Answer:
What's the question you need help on?
 
        
                    
             
        
        
        
56,900 but I'm only 50% sure I don't know about the other 50% sorry If its wrong.