Let x be the total number of beavers. We mark 119 out of x beavers. Then, we found 39 marked beaver out of 89 caught beavers. So, if we build the proportion
we get, solving for x,
So, it is reasonable to suppose that there are about 272 beavers in total. Note that this is an estimate, both numerically and conceptually, since we have no information about the set of beavers caught at the beginning and the end of our experiment.
The slope (change in y/change in x) of the line is (1560 - 1200)/(52 - 40), which is equal to 30. We can plug this into the equation y = mx + b using either the point (40, 1200) or (52, 1560). The slope is represented by m and the y - intercept by b. Therefore, the two possible equations you could use are:
1200 = 30(40) + b
or 1560 = 30(52) + b
Using either equation, you'll get that b is equal to 0, which makes sense in the context of the problem, since it's reasonable to expect that the labor expenses would be 0 for 0 hours worked.