Which of the following describes a relationship of mutualism? question 20 options: a. oxpecker birds eat parasitic ticks off the backs of zebras b. a tapeworm latches itself in the intestines of a rat, feeding off all the nutrients eaten by the rat c. a polar bear catches a seal for dinner d. birds feed off the insects that are stirred up from the grasses as cattle move through save

Mutualism is a symbiotic relationship in which both organisms benefit.
In A, the Oxpecker birds benefit since they get food, and the zebras benefit since they get ticks removed from them. This is mutualism.
In B, this is parasitism since the tapeworm is benefiting from getting nutrients but the rat is being harmed from having its nutrients stolen from it.
C is an example of a predator-prey relationship since the polar bear is eating the seal.
D is an example of commensalism since the birds are getting food from the cattle stirring through the grass but the cows don't care about the birds taking the insects.

So the answer is A.

Maybe you meant 45 cubic feet which is a unit for volume. If it is a unit of area, then other data might be needed.

Assuming 45 cubic feet is the volume of the tank,

Solving for the density in terms of number of goldfish per cubic feet of the tank:
 
density = number of goldfish per cubic feet of the tank
density = 12 goldfishes / 45 cubic feet = 0.27 goldfish/cubic feet of the tank