Hey guys!

Here's a question on a math test (with solutions) that I don't understand very well:

So for the first step, i understand what they did, and how they got the point on the graph.

For the second step, i see they pulled out $\displaystyle 4x$ and i understand how they get $\displaystyle 3y^2y'$ but i dont understand how they got $\displaystyle 4y^3$ and $\displaystyle 15y^2y'$

could anyone help me with that?