a triangular prism Has triple the volume than the volume of a rectangular prism, How is that possible?

A . . . (-4, -2)

C . . . (18, -8)

The slope of the line  AC  is  (-8 + 2) / (18 + 4) = -6 / 22  =  -3/11 .
The slope of any line perpendicular to AC is  11/3 .

The midpoint of the line segment AC is  [ 1/2(-4+18), 1/2(-2-8) ]

                                                               =  (7, -5) .

Now you have the slope and one point on the
perpendicular bisector of  AC .

        Slope = 11/3

        Point  =  (7, -5)