Answer
$f'(4)=1$
Work Step by Step
If we zoom in to a point on the graph where $x=4$.
We see that the curve appears to be a straight line as shown in the image of the graph.
We can take the two closest points from the point where $x=4$. And then find the slope using them which will approximately equal to the $f'(4)$ which is the slope of the tangent line at $x=4$.
let the two points be $(4.002,9.002)$ and $(3.998,8.998)$.
Thus slope $= \dfrac{9.002-8.998}{4.002-3.998}=\dfrac{0.004}{0
004}=1$
Hence $f'(4)=1$
