You and Mae are in free-float frames. Mae has just passed you, traveling at a speed of 60 km/hr. You throw a ball toward her at a speed of 60 km/hr. What will Mae see the ball doing?

She will see the ball as if it were at rest. Relative to her she sees the earth moving back at 60km per hr while the ball moves forward at 60 km per hr. Therefore these velocities will "cancel" in her frame of reference and appear as if the ball were still