Question 1197813
Here is how to find one of the points - might not be the best method -


From the left-most given point
some unknown point to find (x,y)
{{{(x-(-8))/(11-(-8))=1/4}}}
{{{x=-3&1/4}}}
-
{{{(y-1)/(7-1)=1/4}}}
{{{y=2&1/2}}}
-
This point,  ( -13/4, 5/2)


Handle the other two unknown points in like manner.


The point found was not rechecked too carefully.