<image> Cars A and B start simultaneously from point $$M$$ and travel at their respective constant speeds towards point $$N$$. Car A reaches point $$N$$ first, stops for $$1h$$, and then returns at its original speed until it meets car B. The speed of car B is $$50km/h$$. The graph shows the function of the distance $$y(km)$$ between the two cars and the travel time of car B $$x(h)$$.
$$(1)$$ The speed of car A is ______ $$km/h$$, and the distance between points $$M$$ and $$N$$ is ______ $$km$$;
$$(2)$$ Determine the time car B has traveled when the two cars meet;
$$(3)$$ Find the equation of the line segment $$AB$$.