At a soccer practice, the players run sprints. they start at the goal, run 10 m toward the center of the field and then run back to the goal. then they run 20 m toward the center of the field and back to the goal. finally they run 30 m toward the center of the field, turn around, and run back to the goal again. one player times herself to try and beat her personal best time. she runs the first 10 m in 2.5 s and gets back to the goal in 2.8 s. then she runs the 20-m sprint in 5.7 s and gets back to the goal in 6.7 s. she runs the final 30-m sprint in 12 s and gets back to the goal in 15 s. what was her average speed for the entire exercise?