Find the derivative of the function using the quotient rule:

Put z = 3.

Simplify, then find the value of f(z) when z = 3.

Then use:

m is f'(3), and c is a constant.

To find c, use y = f(3) and x = z

You'll get your equation of the line now. You can replace y and x by f(z) and z respectively.