Two runners are racing to a turn-around point 6 km away and then back to the starting point. The first runner maintains a constant 3 m/s velocity for the entire out-and-back race. The second runner runs at 7 m/s to the turn-around point and then, totally winded, returns to the starting point at 1.5 m/s. Turning around requires no time. Which runner wins and by how much?