The bit in red is where you are going wrong. You seem to be saying that

, and that is not true. It's the x that is raised to the power 4, not the 5.

It is correct that the derivative of

is

. So for example, if you take x=2, that corresponds to the point (2,32) on the graph of

. The slope at that point is

. The same sort of calculation will give you the slope of the graph for any other value of x.

**Edit.** Deadstar has just said the exact same thing, even using the same example of taking x=2. Coincidence!