Answer:
you would have 100 cats left
You have the right idea so far, but you forgot to finish it up.
Point slope form is
y - y1 = m(x - x1)
where m is the slope, and (x1,y1) is the point the line goes through. As you can see, we have infinitely many choices for (x1,y1). If you use the y intercept point (0,5), then
y - y1 = m(x - x1)
y - 5 = -1(x - 0) ..... this is one of infinitely many possible answers
OR
If you use the point (2,3), then we'd say
y - y1 = m(x - x1)
y - 3 = -1(x - 2) ..... which is another possible answer
There are infinitely many other choices, but I'm only picking the points in which your teacher has shown as big dots.
By the way, nice work on getting the correct answer for the slope-intercept form.
*I'll be keeping the solutions in exact form*
So firstly, square root both sides. This will split the equation into two:

Next, add 1 on each side: 
Next, divide 3 on both sides, and your answers will be 
C is the correct answer, which is the larger the number of students Terrance surveys, better his estimate of the mean will be
School is not a a proper noun so it will start with a lowercase letter