When differentiating, you want to use the formula ax^n differentiates to (an)x^(n-1), so for the example above, x^3 where a is 1, and n is 3, the differentiation is (13)x^(3-1) which results to 3x^2.
This is repeated for x^2 as 2x. For -4x, a = -4 and n = 1 so differentiating this becomes (-41)x^(1-1) which results to -4 as x^0 is 1. When the term does not have an x term like for instance +5, the term can be disregarded. It can be rewritten as 5x^0 and when differentiated, becomes (50)x^0-1. This results in the answer being 0.
The overall answer for this question is dy/dx = 3x^2 + 2x - 4.