This is for the MC II-A course.

Question 7.28 is referring to question 7.8: 

Let $a$ be a real number, and the equation $x^2+a^2x+a=0$ has real roots for $x$. Find the maximum possible root $x$.

The solution to Question 7.8 is in the lecture video, and also available in the book.  Question 7.28 is an additional question based on that.

To James Shi: Good! This is the same question in MC III.  There are multiple practices with this technique and I hope everyone learns the mathematical ideas behind it.