Assume that segment r exerts a force of magnitude t on segment l. what is the magnitude flr of the force exerted on segment r by segment l?

If we are talking on the force being exerted by a segment of a rope of lenght R on the right on a point M which is being also pulled from the Left by a segment of rope R  as shown in the figure attached. Then we invoke Newton's Third Law:
"Any force exerted by an object (in this case a segment of the rope) also suffers a equal and opposite force".
If we pick whis is the tension exerted by the right segment then the left segment will also exert an equal and opposite force so we have that

The answer is a 0.64 volts