Answer
$f = 5 - 3x $
$c = 1$
Work Step by Step
We have that $f'(c) = \lim\limits_{∆x \to 0}$ $\frac{[5 - 3(1 + ∆x)] - 2 }{∆x}$.
Taken the original formula $f'(x) = \lim\limits_{∆x \to 0}$ $\frac{f(x + ∆x) - f(x)}{∆x}$, which is equal to
$f'(c) = \lim\limits_{∆x \to 0}$ $\frac{f(c + ∆x) - f(c)}{∆x}$, we have that
$f(c + ∆x) = 5 - 3(1 + ∆x)$
Then, we can conclude that $f = 5 - 3x$ and $c = 1$
