I need the answer to this please and I need the steps written out please.

Question

Thirty alligators were captured in the Louisiana bayou (swamp) and tagged by National Park Officials and then put back in the bayou. One month later. Fifty alligators were captured from the same part of the bayou. Eighteen of which had been tagged. Estimate to the nearest whole number how many alligators are in that part of Louisiana. 

Answer 1

N alligators in the swamp... 30 of them are tagged and released

Therefore there are N-30 untagged gators...

A sample of 50 is taken from the population.

18 of them are tagged, so 32 are not tagged

18/30 = 32/(n-30)

cross multiplies:

18(n-30) = 32*30

18n - 540 = 960

18n = 1500

n = 1500/18 = 750/9 = 250/3 = 83 and 1/3

so 85 gators in the swap