Answer:
Ta fácil le quedan 5 kilos :v de que grado es esto._.
I wrote the steps down, hopefully you understand them and the answer is on the lower right corner.
You first must find the 18% of the fish population.
You multiply 500 by .18 . You are supposed to get 90.
90 is the 18% fish increase.
Then you just add 500 + 90 and you will get 590 fish that are now in the school.