A lamp attached to a balloon rises vertically at 0.50 m/s while directly above a point P on level ground. At the moment the lamp is 10 m above P, a runner who is 1.7 m tall is 10 m from P and moving directly away from P at 4.0 m/s. Determine the instantaneous speed (in m/s) of the tip of the runner’s shadow along the ground at that moment.