Derivatives Plz Help I'm close to dropping but this is required

Question

If f (x) = 4

then f ' (3) =

Answer 1

The derivative is a function where you plug in an x-value and out comes the slope of the tangent line for f(x) at this x-value.

f(x) = 4 is a horizontal line (y does not change, it is always 4). What is the slope of a horizontal line everywhere. Answer, it is always 0. So f'(x) =0 . Then what is f'(3) = ?