30 I think because 6 12 18 24 30 and 10 20 30
The midpoint formula for a segment is:

apply to points R and P

using the definition of slope find the slope of the segment

apply to points R and P

to lines are parallel when the slopes are the same

two lines are perpendicular when the product of the slopes is equal to -1
It is true. Guptas did figure out the earth was round by observing lunar eclipses.