critical points at (57.735,5000) and (-57.735,5000). Neither of these
are in the feasible region.
As the constraints are of strict inequality type there is no point in
the faesible region at which R(x,y) takes a maximal value.
If the constraints were:
x>=0, y>=0, and 8x+3y<=2400,
then the maximum would occur on the boundary of the feasible region, and
one could find it by examining R(x,y) on the boundary.