Judging from this problem, do you happen to go to university in Calgary?
Hehe, anyways.... I missed a class (snow), so hopefully I'm close to the proper method.
(a)Anyhow, it's asking for slope, so
. Here, lets put and
So, after this, I would get rid of the fraction in the top, and simplify enough to get the form they are asking for. Should work out perfect. And as for the rest, if you think of it with the slope idea, it should come naturally to you.
(b) Using the equation you got from the last part, solve the limit as x approaches 4 for it.
(c) Substitute the slope, an x value, and a y value in and solve for b. That will give you your equation. (the y and x value are given, the slope you calculated)
And if anyone else sees something wrong with my methods or work, feel free to correct.