If T is the midpoint of line segment SR then we can write the coords of S as (x,y) and T, being the midpoint, has to come in between S and R so the average of the x and y coords=(x-14)/2 and (y+20)/2 are respectively -17 and 16. So (x-14)/2=-17; x-14=-34; x=-20 and (y+20)/2=16, so y=32-20=12. The coords of S are (-20,12).