The density of a fish tank is 0.2fish over feet cubed. there are 8 fish in the tank. what is the volume of the tank? 4 ft3 16 ft3 32 ft3 40 ft3

For this case the density is given by:
 D = fish / volume
 By clearing the volume we have:
 volume = fish / D
 Substituting values:
 volume = (8) / (0.2)
 volume = 40 feet ^ 3
 
 the volume of the tank is:
 40 ft3

The length of what is left would be 1 1/2 feet long.