Awildlife service wanted to estimate the number of alligators in a river so they tagged 90 alligators and released them back into the river. later they found that a sample of 200 alligators contained 23 that were tagged. assuming that the tagged alligators are evenly distributed, what is the best estimate of the number of alligators in the river?

this is from a practice test i found online for a placement test for a community college. i have never encountered these type of word problems before. i don't even know where to start.