SAT math practice question: Properties of parabolas

 
Try the following SAT math practice question (No Calculator) that tests your understanding of properties of parabolas in the coordinate plane.

Question(No Calculator): In the $xy$-coordinate plane, $A$ and $B$ are different points that have the same $y$-coordinate and lie on the parabola whose equation is $y = x^2-3x-20$. What is the $x$-coordinate of the midpoint of $\overline{AB}$ ?

1. $\quad 0$
2. $\quad \displaystyle \frac{1}{2}$
3. $\quad 1$
4. $\quad \displaystyle \frac{3}{2}$