First of all, the midline is a horizontal line. As such, it will have an equation like [tex] y=k [/tex], and we have to find the correct value for [tex] k [/tex].
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
[tex] \dfrac{2+6}{2} = 4 [/tex]
