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.

Data from 2005 for various age groups show that for each $100 increase in the median weekly income for whites, the median weekly income of blacks increases by $105. also, for workers of ages 25 to 54 the median weekly income for whites was $676 and for blacks was $527. (a) let w represent the median weekly income for whites and b the median weekly income for blacks, and write the equation of the line that gives b as a linear function of w. b = (b) when the median weekly income for whites is $760, what does the equation in (a) predict for the median weekly income for blacks?