Answer: Reciprocal altruism
Explanation:
When you out your time and effort in doing something for someone and you also expect that they will also do that in return this is called reciprocal altruism.
It is like giving back just as someone has given to you .
I do you a favour and you also do me a favour when I am in need of a favour.
Coral helps Alex to study for her physics exam, she can do the same thing by helping him now study for his genetic exam as he also did out his own will for her.