First of all, the midline is a horizontal line. As such, it will have an equation like
, and we have to find the correct value for
.
To find it, we have to take the average of the y-coordinates of the min and max points.
Since the maximum is 6 and the minimum is 2, the average is
![(2+6)/(2) = 4](https://img.qammunity.org/2020/formulas/mathematics/college/pafskjrupagxl1gyps4c2fvajs0va6o5bi.png)