ANSWER
The coordinates of point R in the first quadrant are
.
Step-by-step explanation
We were given that the hypotenuse of the right angle triangle has vertices
and
.
The third point R is the intersection of the horizontal line that passes through
, that has equation
and the vertical line that passes through
which also has equation
.
Hence one possible coordinates of point R is
which lies in the first quadrant.
The third point T could also be the intersection of the vertical line that passes through
, that has equation
and the horizontal line that passes through
which also has equation
.
Hence another possible coordinates of point R is
which lies in the third quadrant.
Therefore the required coordinates of R is

See diagram in attachment