$$\frac{dy}{dx} =\sqrt{7x^3}$$
I need to use substitution on the $7x^3$ but I'm a little stuck. My car broke down on the way to class and I missed the lesson!
I get this far..
$$u =7x^3$$ $$du = 21x^2 dx$$ $$dx = \frac{du}{21x^2}$$ $$dy = \sqrt{u} \frac{du}{21x^2}$$