Reasoning:  the distance from one endpoint to the
midpoint of a line is one-half the distance to the
other endpoint, so find one-half the distance and 
multiply it by 2.

use the distance formula:



where (x1,y1) = (-3,1) and (x2,y2) = (8,2)

to find half the distance. 

Then multiply what you get by 2.

Edwin